UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

FORM 10-K

Commission file number 1-14023

Corporate Office Properties Trust
(Exact name of registrant as specified in its charter)

Registrant's telephone number, including area code: (443) 285-5400

Securities registered pursuant to Section 12(b) of the Act:

Securities registered pursuant to Section 12(g) of the Act: None

          Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. ý Yes    o No

          Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Exchange Act. o Yes    ý No

          Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. ý Yes    o No

          Indicate by check mark whether the registrant has submitted electronically and posted on its corporate web site, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files). o Yes    o No

          Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K is not contained herein, and will not be contained, to the best of registrant's knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K. o

          Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See the definitions of "large accelerated filer," "accelerated filer" and "smaller reporting company" in Rule 12b-2 of the Exchange Act. (Check One):

          Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act.) o Yes    ý No

          The aggregate market value of the voting and nonvoting common equity held by non-affiliates of the registrant was approximately $1.7 billion, as calculated using the closing price of the common shares of beneficial interest on the New York Stock Exchange and our outstanding shares as of June 30, 2009. For purposes of calculating this amount only, affiliates are defined as Trustees, executive owners and beneficial owners of more than 10% of the registrant's outstanding common shares of beneficial interest, $0.01 par value. At January 29, 2010, 58,385,958 of the registrant's common shares of beneficial interest were outstanding.

          Portions of the annual shareholders' report of the registrant for the year ended December 31, 2009 are incorporated by reference into Parts I and II of this Form 10-K and portions of the proxy statement of the registrant for its 2010 Annual Meeting of Shareholders to be filed within 120 days after the end of the fiscal year covered by this Form 10-K are incorporated by reference into Part III of this Form 10-K.

Table of Contents

Table of Contents
Form 10-K

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FORWARD-LOOKING STATEMENTS

        This Form 10-K contains "forward-looking" statements, as defined in the Private Securities Litigation Reform Act of 1995, that are based on our current expectations, estimates and projections about future events and financial trends affecting the financial condition and operations of our business. Forward-looking statements can be identified by the use of words such as "may," "will," "should," "expect," "estimate," "plan" or other comparable terminology. Forward-looking statements are inherently subject to risks and uncertainties, many of which we cannot predict with accuracy and some of which we might not even anticipate. Although we believe that the expectations, estimates and projections reflected in such forward-looking statements are based on reasonable assumptions at the time made, we can give no assurance that these expectations, estimates and projections will be achieved. Future events and actual results may differ materially from those discussed in the forward-looking statements. Important factors that may affect these expectations, estimates and projections include, but are not limited to:

•

general economic and business conditions, which will, among other things, affect office property demand and rents, tenant creditworthiness, interest rates and financing availability;



•

adverse changes in the real estate markets including, among other things, increased competition with other companies;



•

our ability to borrow on favorable terms;



•

risks of real estate acquisition and development activities, including, among other things, risks that development projects may not be completed on schedule, that tenants may not take occupancy or pay rent or that development and operating costs may be greater than anticipated;



•

risks of investing through joint venture structures, including risks that our joint venture partners may not fulfill their financial obligations as investors or may take actions that are inconsistent with our objectives;



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our ability to satisfy and operate effectively under Federal income tax rules relating to real estate investment trusts and partnerships;



•

governmental actions and initiatives; and



•

environmental requirements.

        For further information on factors that could affect the company and the statements contained herein, you should refer to the section below entitled "Item 1A. Risk Factors." We undertake no obligation to update or supplement forward-looking statements.

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PART I

Item 1.    Business

OUR COMPANY

        General.    We are a specialty office real estate investment trust ("REIT") that focuses primarily on strategic customer relationships and specialized tenant requirements in the United States Government, defense information technology and data sectors. We acquire, develop, manage and lease properties that are typically concentrated in large office parks primarily located adjacent to government demand drivers and/or in demographically strong markets possessing growth opportunities. As of December 31, 2009, our investments in real estate included the following:

•

249 wholly owned operating properties in Maryland, Virginia, Colorado, Texas, Pennsylvania and New Jersey containing 19.1 million square feet that were 90.7% occupied;



•

17 wholly owned office properties under construction, development or redevelopment that we estimate will total approximately 2.1 million square feet upon completion;



•

wholly owned land parcels totaling 1,521 acres that were predominantly located near certain of our operating properties and that we believe are potentially developable into approximately 13.5 million square feet; and



•

partial ownership interests through joint ventures in the following:



•

20 operating properties containing approximately 1.1 million square feet that were 70.9% occupied;



•

356,000 square feet in one property that was under redevelopment; and



•

land parcels totaling 297 acres (including 56 acres under contract in one joint venture) that were predominantly located near certain of our operating properties and potentially developable into approximately 3.1 million square feet.

        We conduct almost all of our operations through our operating partnership, Corporate Office Properties, L.P. (the "Operating Partnership"), a Delaware limited partnership, of which we are the managing general partner. The Operating Partnership owns real estate both directly and through subsidiaries. The Operating Partnership also owns 100% of a number of entities that provide real estate services such as property management, construction and development and heating and air conditioning services primarily for our properties, but also for third parties.

        Interests in our Operating Partnership are in the form of common and preferred units. As of December 31, 2009, we owned 91.7% of the outstanding common units and 95.8% of the outstanding preferred units in our Operating Partnership. The remaining common and preferred units in our Operating Partnership were owned by third parties, which included certain of our Trustees.

        We believe that we are organized and have operated in a manner that permits us to satisfy the requirements for taxation as a REIT under the Internal Revenue Code of 1986, as amended, and we intend to continue to operate in such a manner. If we qualify for taxation as a REIT, we generally will not be subject to Federal income tax on our taxable income that is distributed to our shareholders. A REIT is subject to a number of organizational and operational requirements, including a requirement that it distribute to its shareholders at least 90% of its annual taxable income (excluding net capital gains).

        Our executive offices are located at 6711 Columbia Gateway Drive, Suite 300, Columbia, Maryland 21046 and our telephone number is (443) 285-5400.

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        Our Internet address is www.copt.com. We make available on our Internet website free of charge our annual reports on Form 10-K, quarterly reports on Form 10-Q, current reports on Form 8-K and amendments to those reports filed or furnished pursuant to Section 13(a) or 15(d) of the Exchange Act as soon as reasonably possible after we file such material with the Securities and Exchange Commission (the "SEC"). In addition, we have made available on our Internet website under the heading "Corporate Governance" the charters for our Board of Trustees' Audit, Nominating and Corporate Governance and Compensation Committees, as well as our Corporate Governance Guidelines, Code of Business Conduct and Ethics and Code of Ethics for Financial Officers. We intend to make available on our website any future amendments or waivers to our Code of Business Conduct and Ethics and Code of Ethics for Financial Officers within four business days after any such amendments or waivers. The information on our Internet site is not part of this report.

        The SEC maintains an Internet website that contains reports, proxy and information statements and other information regarding issuers that file electronically with the SEC. This Internet website can be accessed at www.sec.gov. The public may also read and copy paper filings that we have made with the SEC at the SEC's Public Reference Room, located at 100 F Street, NE, Washington, D.C. 20549. Information on the operation of the Public Reference Room may be obtained by calling (800) SEC-0330.

Significant 2009 Developments

        During 2009, we:

•

finished the period with our wholly owned portfolio of properties 90.7% occupied;



•

acquired a 474,000 square foot office tower, a parking lot, a utility distribution center, four waterfront lots and riparian rights, all of which are part of the Canton Crossing planned unit development in Baltimore, Maryland. We completed this acquisition for an aggregate cost of $123.2 million;



•

acquired two additional properties totaling 223,000 square feet that were 100% leased upon acquisition and land that we believe can support approximately 95,000 developable square feet for $50.5 million;



•

placed into service an aggregate of 759,000 square feet in newly constructed space located in ten properties;



•

closed on $348.4 million in new borrowings; and



•

issued 2.99 million common shares in an underwritten public offering made in conjunction with our inclusion in the S&P MidCap 400 Index effective April 1, 2009. The shares were issued at a public offering price of $24.35 per share for net proceeds of $72.1 million after underwriting discounts but before offering expenses.

Business and Growth Strategies

        Our primary objectives are to achieve sustainable long-term growth in results of operations and to maximize long-term shareholder value. This section sets forth key components of our business and growth strategies that we have in place to support these objectives.

Business Strategies

        Customer Strategy:    We believe that we differentiate ourselves by being a real estate company that does not view space in properties as its primary commodity. Rather, we focus our operations on serving the needs of our customers and enabling them to be successful. This strategy includes a focus on establishing and nurturing long-term relationships with quality tenants and accommodating their multi-

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locational needs. It also includes a focus on providing a level of service that exceeds customer expectations both in terms of the quality of the space we provide and our level of responsiveness to their needs. In 2009, we won the CEL & Associates, Inc. award for quality service and tenant satisfaction among nationwide office operators in the large owner category for the sixth consecutive year. We believe that operating with such a consistent emphasis on service enables us to be the landlord of choice with high quality customers and contributes to high levels of customer loyalty and retention.

        Our focus on tenants in the United States Government, defense information technology and data sectors is another key aspect of our customer strategy. A high percentage of our revenue is derived from these customers, and we believe that we are well positioned for future growth through such customers for reasons that include the following:

•

our strong relationships and reputation for high service levels that we have forged over the years and continue to emphasize;



•

the proximity of our properties to government demand drivers (such as military installations) in various regions of the country and our willingness to expand to other regions where demand exists; and



•

the depth of our collective team knowledge, experience and capabilities in developing and operating data centers and secure properties that meet the United States Government's Force Protection requirements.

        Market Strategy:    We focus on owning properties where our tenants want to be, which in the case of the United States Government and defense information technology customers is mostly near government demand drivers. We also concentrate our operations in markets and submarkets that are located where we believe we already possess, or can effectively achieve, the critical mass necessary to maximize management efficiencies, operating synergies and competitive advantages through our acquisition, property management, leasing and development activities. The attributes we look for in selecting markets and submarkets include, among others: (1) proximity to large demand drivers; (2) strong demographics; (3) attractiveness to high quality tenants; (4) potential for growth and stability in economic down cycles; (5) future acquisition and development opportunities; and (6) minimal competition from other long-term office property owners. We typically focus on owning and operating properties in large business parks located outside of central business districts. We believe that such parks generally attract long-term, high-quality tenants seeking to attract and retain quality work forces because they are typically situated along major transportation routes with easy access to support services, amenities and residential communities.

        Capital Strategy:    Our capital strategy is aimed at maintaining a flexible capital structure in order to facilitate growth and performance in the face of differing market conditions in the most cost-effective manner by:

•

using debt comprised primarily of mortgage loans and our unsecured revolving credit facility;



•

using equity raised through issuances of common and preferred shares of beneficial interest, issuances of common and preferred units in our Operating Partnership and, to a lesser extent, joint venture structures for certain investments;



•

conservatively managing our debt by monitoring, among other things: our debt levels relative to our overall capital structure; the relationship of certain measures of earnings to certain financing cost requirements (commonly referred to as coverage ratios); the relationship of our total

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variable-rate debt to our total debt; and the timing of debt maturities to ensure that maturities in any year do not exceed levels that we believe we can refinance; and

•

continuously evaluating the ability of our capital resources to accommodate our plans for future growth.

        Environmentally Responsible Development and Management Strategy:    We are focused on developing and operating our properties in a manner that minimizes global impact and have been committed to this effort since 2003. This strategy includes:

•

constructing new "Green" buildings that are designed to use resources with a higher level of efficiency and lower impact on human health and the environment during their life cycle than conventional buildings. An example of our focus in this area is our participation in the United States Government's Leadership in Energy and Environmental Design ("LEED") program, which has a rigorous certification process for evaluating and rating "Green" buildings in order for such buildings to qualify for the program's Certified, Silver, Gold and Platinum ratings;



•

retrofitting select existing properties to also become "Green"; and



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using "Green" operating and purchase practices and housekeeping standards in managing our properties.

We believe that our commitment to this strategy is evident in the fact that as of December 31, 2009, we had seven buildings certified LEED Gold, nine buildings certified LEED Silver, one building certified LEED and 36 other buildings registered for LEED Silver or Gold certification, and we had 16 professionals on staff who hold the LEED Accredited Professional designation. We also have established an internal goal to have 50% of our portfolio be "Green" buildings by 2015. We believe that this strategy is important not just because our customers will demand it, but also because it is simply the right thing to do.

Growth Strategies

        Acquisition and Property Development Strategy:    We pursue acquisition and property development opportunities for properties that support our customer and market strategies discussed above. As a result, the focus of our acquisition and development activities generally include properties that:

•

are located near demand drivers that we believe are attractive to customers in the United States Government, defense information technology and data sectors;



•

are located in markets or submarkets that we believe meet the criteria set forth above in our market strategy; or



•

do not align with our customer or market strategies but represent situations that we believe provide high opportunity for favorable risk-adjusted returns on investment.

        We typically seek to make acquisitions at attractive yields and below replacement cost. We also seek to increase operating cash flow of certain acquisitions by repositioning the properties and capitalizing on existing below market leases and expansion opportunities. We pursue development activities as market conditions and leasing opportunities support favorable risk-adjusted returns.

        Internal Growth Strategy:    We aggressively manage our portfolio to maximize the operating performance of each property through: (1) proactive property management and leasing; (2) achieving operating efficiencies through increasing economies of scale and, where possible, aggregating vendor contracts to achieve volume pricing discounts; and (3) renewing tenant leases and re-tenanting at increased rents where market conditions permit.

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Industry Segments

        We operate in one primary industry: commercial office real estate. At December 31, 2009, our commercial office real estate operations had nine primary geographical segments, as set forth below:

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Baltimore/Washington Corridor (generally defined as the Maryland counties of Howard and Anne Arundel);



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Northern Virginia (defined as Fairfax County, Virginia);



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Suburban Maryland (defined as the Maryland counties of Montgomery, Prince George's and Frederick);



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St. Mary's & King George Counties (in Maryland and Virginia, respectively);



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Greater Baltimore, Maryland (generally defined as the Maryland counties of Baltimore and Harford and Baltimore City);



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Colorado Springs, Colorado;



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San Antonio, Texas;



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Greater Philadelphia, Pennsylvania; and



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Central New Jersey.

        As of December 31, 2009, 147 of our wholly owned properties were located in what is widely known as the Greater Washington, D.C. region, which includes the first four regions set forth above, and 64 were located in neighboring Greater Baltimore. At December 31, 2009, we also owned 21 wholly owned properties in Colorado Springs and six in San Antonio. In addition, we owned five properties in total as of December 31, 2009 in the last two locations set forth above that are considered non-core to the Company. For information relating to these geographic segments, you should refer to Note 15 to our Consolidated Financial Statements, which is included in a separate section at the end of this Annual Report on Form 10-K beginning on page F-1.

Employees

        As of December 31, 2009, we had 382 employees, none of whom were parties to collective bargaining agreements. We believe that our relations with our employees are good.

Competition

        The commercial real estate market is highly competitive. Numerous commercial properties compete with our properties for tenants. Some of the properties competing with ours may be newer or have more desirable locations, or the competing properties' owners may be willing to accept lower rents than are acceptable to us. In addition, the competitive environment for leasing is affected considerably by a number of factors including, among other things, changes in economic factors and supply and demand of space. These factors may make it difficult for us to lease existing vacant space and space associated with future lease expirations at rental rates that are sufficient to meeting our short-term capital needs.

        We also compete for the acquisition of commercial properties with many entities, including other publicly-traded commercial REITs. Many of our competitors for such acquisitions have substantially greater financial resources than ours. In addition, our competitors may be willing to accept lower returns on their investments. If our competitors prevent us from buying properties that we have targeted for acquisition, we may not be able to meet our property acquisition goals.

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Item 1A.    Risk Factors

        Set forth below are risks and uncertainties relating to our business and the ownership of our securities. You should carefully consider each of these risks and uncertainties and all of the information in this Annual Report on Form 10-K and its Exhibits, including our Consolidated Financial Statements and notes thereto for the year ended December 31, 2009, which are included in a separate section at the end of this report beginning on page F-1.

        Our performance and value are subject to risks associated with our properties and with the real estate industry.    Real estate investments are subject to various risks and fluctuations in value and demand, many of which are beyond our control. Our economic performance and the value of our real estate assets may decline due to conditions in the general economy and the real estate business which, in turn, could have an adverse effect on our financial position, results of operations, cash flows and ability to make expected distributions to our shareholders. These conditions include, but are not limited to:

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downturns in national, regional and local economic environments, including increases in the unemployment rate and inflation or deflation;



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competition from other office properties;



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deteriorating local real estate market conditions, such as oversupply, reduction in demand for office space and decreasing rental rates;



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increasing vacancies and the need to periodically repair, renovate and re-lease space;



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adverse developments concerning our tenants, which could affect our ability to collect rents and execute lease renewals;



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increasing operating costs, including insurance expense, utilities, real estate taxes and other expenses, much of which we may not be able to pass through to tenants;



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increasing interest rates and unavailability of financing on acceptable terms or at all;



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adverse changes in taxation or zoning laws;



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our potential inability to secure adequate insurance;



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adverse consequences resulting from civil disturbances, natural disasters, terrorist acts or acts of war; and



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potential liability under environmental or other laws or regulations.

        We may suffer adverse consequences as a result of recent and future economic events.    Since the latter part of 2007, the United States and world economies have struggled through difficult conditions, including a significant recession. This slowdown has had devastating effects on the capital markets, with tightening credit availability. The commercial real estate industry was affected by these events over the last three years and, we believe, will likely continue to be affected at least through 2010. These events could adversely affect us in numerous ways discussed throughout this Annual Report on Form 10-K. The real estate industry in general has encountered increased difficulty in obtaining capital to fund growth activities, such as acquisitions and development costs, debt repayments and other capital requirements. As a result, the level of risk that we may not be able to obtain new financing for acquisitions, development activities, refinancing of existing debt or other capital requirements at reasonable terms, if at all, has increased. We believe that there is an increased likelihood in the current economic climate of tenants encountering financial difficulties, including bankruptcy, insolvency or general downturn of business, and as a result there is an increased likelihood of such tenants defaulting in their lease obligations to us. We also expect that our leasing activities will be adversely affected, with an increasing likelihood of our being unsuccessful in renewing tenants, renewing tenants on terms less

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favorable to us or being unable to lease newly constructed space. As a result, the conditions brought about by these economic events could collectively have an adverse effect on our financial position, results of operations, cash flows and ability to make expected distributions to our shareholders.

        We are dependent on external sources of capital for future growth.    Because we are a REIT, we must distribute at least 90% of our annual taxable income to our shareholders. Due to this requirement, we are not permitted to significantly fund our acquisition, construction and development activities using cash flow from operations. Therefore, our ability to fund these activities is dependent on our ability to access capital funded by third parties. Such capital could be in the form of new debt, equity issuances of common shares, preferred shares, common and preferred units in our Operating Partnership or joint venture funding. These capital sources may not be available on favorable terms or at all. Since the United States financial markets have recently experienced extreme volatility and, as a result, credit markets have tightened considerably, the level of risk that we may not be able to obtain new financing for acquisitions, development activities or other capital requirements at reasonable terms, if at all, in the near future has increased. Moreover, additional debt financing may substantially increase our leverage and subject us to covenants that restrict management's flexibility in directing our operations, and additional equity offerings may result in substantial dilution of our shareholders' interests. Our inability to obtain capital when needed could have a material adverse effect on our ability to expand our business and fund other cash requirements.

        We use our Revolving Credit Facility to initially finance much of our investing and financing activities. We also use our Revolving Construction Facility and other credit facilities to fund a significant portion of our construction activities. Our lenders under these and other facilities could, for financial hardship or other reasons, fail to honor their commitments to fund our requests for borrowings under these facilities. In the event that one or more lenders under these facilities are not able or willing to fund a borrowing request, it would adversely affect our ability to access borrowing capacity under these facilities, which would in turn adversely affect our financial condition, cash flows and ability to make expected distributions to our shareholders.

        We may suffer adverse consequences as a result of our reliance on rental revenues for our income.    We earn revenue from renting our properties. Our operating costs do not necessarily fluctuate in relation to changes in our rental revenue. This means that our costs will not necessarily decline and may increase even if our revenues decline.

        For new tenants or upon lease expiration for existing tenants, we generally must make improvements and pay other leasing costs for which we may not receive increased rents. We also make building-related capital improvements for which tenants may not reimburse us.

        If our properties do not generate revenue sufficient to meeting our operating expenses and capital costs, we may have to borrow additional amounts to cover these costs. In such circumstances, we would likely have lower profits or possibly incur losses. We may also find in such circumstances that we are unable to borrow to cover such costs, in which case our operations could be adversely affected. Moreover, there may be less or no cash available for distributions to our shareholders.

        In addition, the competitive environment for leasing is affected considerably by a number of factors including, among other things, changes due to economic factors and supply and demand of space. These factors may make it difficult for us to lease existing vacant space and space associated with future lease expirations at rental rates that are sufficient to meeting our short-term capital needs.

        We rely on the ability of our tenants to pay rent and would be harmed by their inability to do so.    Our performance depends on the ability of our tenants to fulfill their lease obligations by paying their rental payments in a timely manner. If one or more of our major tenants, or a number of our smaller tenants, were to experience financial difficulties, including bankruptcy, insolvency or general downturn

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of business, there could be an adverse effect on financial position, results of operations, cash flows and ability to make expected distributions to our shareholders.

        Adverse developments concerning some of our major tenants and sector concentrations could have a negative impact on our revenue.    As of December 31, 2009, our 20 largest tenants accounted for 55.4% of the total annualized rental revenue of our wholly owned properties, and our three largest of these tenants accounted for 31.5% of that total. We compute the annualized rental revenue by multiplying by 12 the sum of monthly contractual base rents and estimated monthly expense reimbursements under active leases in our portfolio of wholly owned properties as of December 31, 2009. Information regarding our three largest tenants is set forth below:

(1)

Includes affiliated organizations and agencies and predecessor companies.

        Most of our leases with the United States Government provide for a series of one-year terms or provide for early termination rights. The United States Government may terminate its leases if, among other reasons, the United States Congress fails to provide funding. If any of our three largest tenants fail to make rental payments to us or if the United States Government elects to terminate several of its leases and the space cannot be re-leased on satisfactory terms, there would be an adverse effect on our financial performance and ability to make distributions to our shareholders.

        As of December 31, 2009, our properties that were occupied primarily by tenants in the United States Government, defense information technology and data sectors accounted for 54.9% of the total annualized rental revenue of our wholly owned properties. We expect to increase our reliance on these sectors for revenue. A reduction in government spending targeting these sectors could affect the ability of these tenants to fulfill lease obligations or decrease the likelihood that these tenants will renew their leases. Such occurrences could have an adverse effect on our results of operations, financial condition, cash flows and ability to make distributions to our shareholders. We classified the revenue from our leases into this sector grouping based solely on management's knowledge of the tenants' operations in leased space. Occasionally, classifications require subjective and complex judgments. We do not use independent sources such as Standard Industrial Classification codes for classifying our revenue into sector groupings and if we did, the resulting groupings would be materially different.

        Most of our properties are geographically concentrated in the Mid-Atlantic region, particularly in the Greater Washington, D.C. region and neighboring Greater Baltimore, or in particular office parks. We may suffer economic harm in the event of a decline in the real estate market or general economic conditions in those regions or parks.    Most of our properties are located in the Mid-Atlantic region of the United States and, as of December 31, 2009, our properties located in the Greater Washington, D.C. region and neighboring Greater Baltimore accounted for a combined 86.2% of our total annualized rental revenue from wholly owned properties. Our properties are also typically concentrated in office parks in which we own most of the properties. Consequently, we do not have a broad geographic distribution of our properties. As a result, a decline in the real estate market or general economic conditions in the Mid-Atlantic region, the Greater Washington, D.C. region or the office parks in which our properties are located could have an adverse effect on our financial position, results of operations, cash flows and ability to make expected distributions to our shareholders.

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        We would suffer economic harm if we were unable to renew our leases on favorable terms.    When leases expire, our tenants may not renew or may renew on terms less favorable to us than the terms of their original leases. If a tenant vacates a property, we can expect to experience a vacancy for some period of time, as well as incur higher leasing costs than we would likely incur if a tenant renews. As a result, our financial performance and ability to make expected distributions to our shareholders could be adversely affected if we experience a high volume of tenant departures at the end of their lease terms. We expect that the effects of the global downturn on our real estate operations will make our leasing activities increasingly challenging throughout most of 2010 and perhaps beyond and, as a result, there could be an increasing likelihood of our being unsuccessful in renewing tenants or renewing on terms less favorable to us than the terms of the original leases. Set forth below are the percentages of total annualized rental revenue from wholly owned properties as of December 31, 2009 that are subject to scheduled lease expirations in each of the next five years:

        As noted above, most of the leases with our largest tenant, the United States Government, provide for consecutive one-year terms or provide for early termination rights. All of the leasing statistics set forth above assume that the United States Government will remain in the space that it leases through the end of the respective arrangements, without ending consecutive one-year leases prematurely or exercising early termination rights.

        We may encounter a decline in the values of our real estate assets.    The value of our real estate could be adversely affected by general economic and market conditions connected to a specific property, a market or submarket or a broader economic region. Examples of such conditions include a broader economic recession, declining demand for space and decreases in market rental rates and/or market values of real estate assets. If our real estate assets decline in value, it could result in our recognition of impairment losses. Moreover, a decline in the value of our real estate could adversely affect the amount of borrowings available to us under credit facilities and other loans, which could, in turn, adversely affect our cash flows and financial condition.

        We may not be able to compete successfully with other entities that operate in our industry.    The commercial real estate market is highly competitive. We compete for the purchase of commercial property with many entities, including other publicly traded commercial REITs. Many of our competitors have substantially greater financial resources than we do. If our competitors prevent us from buying properties that we target for acquisition, we may not be able to meet our property acquisition goals. Moreover, numerous commercial properties compete for tenants with our properties. Some of the properties competing with ours may be newer or in more desirable locations, or the competing properties' owners may be willing to accept lower rates than are acceptable to us. Competition for property acquisitions, or for tenants in properties that we own, could have an adverse effect on our financial position, results of operations, cash flows and ability to make expected distributions to our shareholders.

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        We may be unable to successfully execute our plans to acquire existing commercial real estate properties.    We intend to acquire existing commercial real estate properties to the extent that suitable acquisitions can be made on advantageous terms. Acquisitions of commercial properties entail risks, such as the risks that we may not be in a position, or have the opportunity in the future, to make suitable property acquisitions on advantageous terms and/or that such acquisitions will fail to perform as expected. The failure of our acquisitions to perform as expected could adversely affect our financial position, results of operations, cash flows and ability to make expected distributions to our shareholders.

        We may be exposed to unknown liabilities from acquired properties.    We may acquire properties that are subject to liabilities in situations where we have no recourse, or only limited recourse, against the prior owners or other third parties with respect to unknown liabilities. As a result, if a liability were asserted against us based upon ownership of those properties, we might have to pay substantial sums to settle or contest it, which could adversely affect our results of operations and cash flow. Examples of unknown liabilities with respect to acquired properties include, but are not limited to:

•

liabilities for clean-up of disclosed or undisclosed environmental contamination;



•

claims by tenants, vendors or other persons dealing with the former owners of the properties;



•

liabilities incurred in the ordinary course of business; and



•

claims for indemnification by general partners, directors, officers and others indemnified by the former owners of the properties.

        We may suffer economic harm as a result of making unsuccessful acquisitions in new markets.    We may pursue selective acquisitions of properties in regions where we have not previously owned properties. These acquisitions may entail risks in addition to those we face in other acquisitions where we are familiar with the regions, such as the risk that we do not correctly anticipate conditions or trends in a new region and are therefore not able to operate the acquired property profitably. If this occurs, it could adversely affect our financial position, results of operations, cash flows and ability to make expected distributions to our shareholders.

        We may be unable to execute our plans to develop and construct additional properties.    Although the majority of our investments are in currently leased properties, we also develop, construct and renovate properties, including some that are not fully pre-leased. When we develop, construct and renovate properties, we assume the risk that actual costs will exceed our budgets, that we will experience delays and that projected leasing will not occur, any of which could adversely affect our financial performance and our ability to make distributions to our shareholders; the risk of projected leasing not occurring has increased as a result of the current economic conditions. In addition, we generally do not obtain construction financing commitments until the development stage of a project is complete and construction is about to commence. We may find that we are unable to obtain financing needed to continue with the construction activities for such projects.

        Certain of our properties containing data centers contain space not suitable for lease other than as data centers, which could make it difficult to reposition them for alternative use.    Certain of our properties contain data center space, which is highly specialized space containing extensive electrical and mechanical systems that are designed uniquely to run and maintain banks of computer servers. As a result, in the event we needed to reposition such data center space for another use, major renovations and expenditures could be required.

        We may suffer adverse effects as a result of the indebtedness that we carry and the terms and covenants that relate to this debt.    Many of our properties are pledged by us to support repayment on indebtedness. In addition, we rely on borrowings to fund some or all of the costs of new property

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acquisitions, construction and development activities and other items. Our organizational documents do not limit the amount of indebtedness that we may incur.

        Payments of principal and interest on our debt may leave us with insufficient cash to operate our properties or pay distributions to our shareholders required to maintain our qualification as a REIT. We are also subject to the risks that:

•

we may not be able to refinance our existing indebtedness, or may refinance on terms that are less favorable to us than the terms of our existing indebtedness;



•

in the event of our default under the terms of our Revolving Credit Facility by us, our Operating Partnership could be restricted from making cash distributions to us, which could result in reduced distributions to our shareholders or the need for us to incur additional debt to fund these distributions; and



•

if we are unable to pay our debt service on time or are unable to comply with restrictive financial covenants in certain of our debt, our lenders could foreclose on our properties securing such debt and, in some cases, other properties and assets that we own.

        Some of our debt is cross-defaulted, which means that failure to pay interest or principal on a loan above a threshold value will create a default on certain of our other loans. In addition, some of our debt which is cross-defaulted also contains cross-collateralization provisions. Any foreclosure of our properties could result in loss of income and asset value that would negatively affect our financial condition, results of operations, cash flows and ability to make expected distributions to our shareholders. In addition, if we are in default and the value of the properties securing a loan is less than the loan balance, we may be required to pay the resulting shortfall to the lender using other assets.

        As of December 31, 2009, 24.8% of our debt had variable interest rates, including the effect of interest rate swaps. If short-term interest rates were to rise, our debt service payments on debt with variable interest rates would increase, which would lower our net income and could decrease our distributions to our shareholders. We use interest rate swap agreements from time to time to reduce the impact of changes in interest rates. Decreases in interest rates would result in increased interest payments due under interest rate swap agreements in place and, in the event we decided to unwind such agreements, could result in our recognizing a loss and remitting a payment.

        We must refinance our debt in the future. As of December 31, 2009, our scheduled debt payments over the next five years, including maturities, were as follows:

        Our operations likely will not generate enough cash flow to repay some or all of this debt without additional borrowings, equity issuances and/or property sales. If we cannot refinance our debt, extend the repayment dates, or raise additional equity prior to the dates when our debt matures, we would

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default on our existing debt, which would have an adverse effect on our financial position, results of operations, cash flows and ability to make expected distributions to our shareholders.

        We have certain distribution requirements that reduce cash available for other business purposes.    As a REIT, we must distribute at least 90% of our annual taxable income (excluding capital gains), which limits the amount of cash we can retain for other business purposes, including amounts to fund acquisitions and development activity. Also, it is possible that because of the differences between the time we actually receive revenue or pay expenses and the period during which we report those items for distribution purposes, we may have to borrow funds to meet the 90% distribution requirement.

        We may be unable to continue to make shareholder distributions at expected levels.    We intend to make regular quarterly cash distributions to our shareholders. However, distribution levels depend on a number of factors, some of which are beyond our control. Some of our loan agreements contain provisions that could restrict future distributions. Our ability to sustain our current distribution level will also be dependent, in part, on other matters, including, but not limited to:

•

continued property occupancy and timely receipt of rent obligations;



•

the amount of future capital expenditures and expenses relating to our properties;



•

the level of leasing activity and future rental rates;



•

the strength of the commercial real estate market;



•

our ability to compete;



•

our costs of compliance with environmental and other laws;



•

our corporate overhead levels;



•

our amount of uninsured losses; and



•

our decision to reinvest in operations rather than distribute available cash.

In addition, we can make distributions to the holders of our common shares only after we make preferential distributions to holders of our preferred shares.

        We may issue additional common or preferred shares that dilute our shareholders' interests.    We may issue additional common shares and preferred shares without shareholder approval. Similarly, we may cause the Operating Partnership to issue its common or preferred units for contributions of cash or property without approval by the limited partners of the Operating Partnership or our shareholders. Our existing shareholders' interests could be diluted if such additional issuances were to occur.

        We may incur additional indebtedness, which may harm our financial position and cash flow and potentially impact our ability to pay dividends on any series of preferred shares.    Our governing documents do not limit us from incurring additional indebtedness and other liabilities. As of December 31, 2009, we had $2.1 billion of consolidated indebtedness outstanding. We may incur additional indebtedness and become more highly leveraged, which could harm our financial position and potentially limit our cash available to pay dividends. As a result, we may not have sufficient funds remaining to satisfy our dividend obligations relating to any series of preferred shares if we incur additional indebtedness.

        Our ability to pay dividends may be limited, and we cannot provide assurance that we will be able to pay dividends regularly.    Because we conduct substantially all of our operations through our Operating Partnership, our ability to pay dividends will depend almost entirely on payments and dividends received on our interests in our Operating Partnership, the payment of which depends in turn on our ability to operate profitably and generate cash flow from our operations. We cannot guarantee that we will be able to pay dividends on a regular quarterly basis in the future. Additionally, the terms

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of some of the debt to which our Operating Partnership is a party limit its ability to make some types of payments and other dividends to us. This in turn limits our ability to make some types of payments, including payment of dividends on common or preferred shares, unless we meet certain financial tests or such payments or dividends are required to maintain our qualification as a REIT. As a result, if we are unable to meet the applicable financial tests, we may not be able to pay dividends on our shares in one or more periods. Furthermore, any new shares of beneficial interest issued will substantially increase the cash required to continue to pay cash dividends at current levels. Any common or preferred shares that may in the future be issued for financing acquisitions, share-based compensation arrangements or otherwise would have a similar effect.

        Our ability to pay dividends on preferred shares is further limited by the requirements of Maryland law.    As a Maryland REIT, we may not under applicable Maryland law make a distribution if either of the following conditions exist after giving effect to the distribution: (1) the REIT would not be able to pay its debts as the debts become due in the usual course of business; or (2) the REIT's total assets would be less than the sum of its total liabilities plus the amount that would be needed, if the REIT were dissolved at the time of the distribution, to satisfy the preferential rights upon dissolution of shareholders whose preferential rights are superior to those receiving the distribution. Therefore, we may not make a distribution on any series of preferred shares if either of the above described conditions exists after giving effect to the distribution.

        Real estate investments are illiquid, and we may not be able to sell our properties on a timely basis when we determine it is appropriate to do so.    Real estate investments can be difficult to sell and convert to cash quickly, especially if market conditions are not favorable, and we may find that to be increasingly the case under the current economic conditions due to a lack of credit availability for potential buyers. Such illiquidity could limit our ability to quickly change our portfolio of properties in response to changes in economic or other conditions. Moreover, under certain circumstances, the Internal Revenue Code imposes certain penalties on a REIT that sells property held for less than two years and limits the number of properties it can sell in a given year. In addition, for certain of our properties that we acquired by issuing units in our Operating Partnership, we are restricted by agreements with the sellers of the properties for a certain period of time from entering into transactions (such as the sale or refinancing of the acquired property) that will result in a taxable gain to the sellers without the seller's consent. Due to these factors, we may be unable to sell a property at an advantageous time.

        We may suffer economic harm as a result of the actions of our joint venture partners.    We invest in certain entities in which we are not the exclusive investor or principal decision maker. As of December 31, 2009, we owned 20 operational properties and one property under redevelopment, and control land for future development, through joint ventures. We also may continue to pursue new investments in real estate through joint ventures. Investments in joint ventures may, under certain circumstances, involve risks not present when a third party is not involved, including the possibility that the other parties to these investments might become bankrupt or fail to fund their share of required capital contributions. Our partners in joint ventures may have economic, tax or other business interests or goals which are inconsistent with our business interests or goals, and may be in a position to take actions contrary to our policies or objectives. Such investments may also lead to impasses, for example, as to whether to sell a property, because neither we nor the other parties to these investments would have full control over the joint venture. In addition, we may in certain circumstances be liable for the actions of the other parties to these investments. Each of these factors could have an adverse effect on our financial condition, results of operations, cash flows and ability to make expected distributions to our shareholders.

        We may need to make additional cash outlays to protect our investment in loans we make that are subordinate to other loans.    We have and may in the future make loans under which we have a

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secured interest in the ownership of a property that is subordinate to other loans on the property. If a default were to occur under the terms of any such loans with us or under the first mortgage loans related to the properties on such loans, we may be in a position where, in order to protect our investment, we would need to either (1) purchase the other loan or (2) foreclose on the ownership interest in the property and repay the first mortgage loan, either of which could have an adverse effect on our financial condition, results of operations, cash flows and ability to make expected distributions to our shareholders.

        We may be subject to possible environmental liabilities.    We are subject to various Federal, state and local environmental laws, including air and water quality, hazardous or toxic substances and health and safety. These laws can impose liability on current and prior property owners or operators for the costs of removal or remediation of hazardous substances released on a property, even if the property owner was not responsible for, or even aware of, the release of the hazardous substances. Costs resulting from environmental liability could be substantial. The presence of hazardous substances on our properties may also adversely affect occupancy and our ability to sell or borrow against those properties. In addition to the costs of government claims under environmental laws, private plaintiffs may bring claims for personal injury or other reasons. Additionally, various laws impose liability for the costs of removal or remediation of hazardous substances at the disposal or treatment facility. Anyone who arranges for the disposal or treatment of hazardous substances at such a facility is potentially liable under such laws. These laws often impose liability on an entity even if the facility was not owned or operated by the entity.

        Although most of our properties have been subject to varying degrees of environmental assessment, many of these assessments are limited in scope and may not include or identify all potential environmental liabilities or risks associated with the property. Identification of new compliance concerns or undiscovered areas of contamination, changes in the extent or known scope of contamination, discovery of additional sites, human exposure to the contamination or changes in cleanup or compliance requirements could result in significant costs to us that could have an adverse effect on our financial condition, results of operations, cash flows and ability to make expected distributions to our shareholders.

        Terrorist attacks, such as those of September 11, 2001, may adversely affect the value of our properties financial position, and cash flows.    We have significant investments in properties located in large metropolitan areas and near military installations. Future terrorist attacks could directly or indirectly damage our properties or cause losses that materially exceed our insurance coverage. After such an attack, tenants in these areas may choose to relocate their businesses to areas of the United States that may be perceived to be less likely targets of future terrorist activity and fewer customers may choose to patronize businesses in these areas. This in turn would trigger a decrease in the demand for space in these areas, which could increase vacancies in our properties and force us to lease space on less favorable terms. As a result, the occurrence of terrorist attacks could adversely affect our financial position, results of operations, cash flows and ability to make expected distributions to our shareholders.

        We may be subject to other possible liabilities that would adversely affect our financial position and cash flows.    Our properties may be subject to other risks related to current or future laws, including laws benefiting disabled persons, state or local laws relating to zoning, construction, fire and life safety requirements and other matters. These laws may require significant property modifications in the future and could result in the levy of fines against us. In addition, although we believe that we adequately insure our properties, we are subject to the risk that our insurance may not cover all of the costs to restore a property that is damaged by a fire or other catastrophic events, including acts of war or, as mentioned above, terrorism. The occurrence of any of these events could have an adverse effect

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on our financial condition, results of operations, cash flows and ability to make expected distributions to our shareholders.

        We may be subject to increased costs of insurance and limitations on coverage, particularly regarding acts of terrorism.    Our portfolio of properties is insured for losses under our property, casualty and umbrella insurance policies through September 30, 2010. These policies include coverage for acts of terrorism. Future changes in the insurance industry's risk assessment approach and pricing structure may increase the cost of insuring our properties and decrease the scope of insurance coverage, either of which could adversely affect our financial position and operating results. Most of our loan agreements contain customary covenants requiring us to maintain insurance. Although we believe that we have adequate insurance coverage for purposes of these agreements, we may not be able to obtain an equivalent amount of coverage at reasonable costs, or at all, in the future. In addition, if lenders insist on greater coverage than we are able to obtain, it could adversely affect our ability to finance and/or refinance our properties and execute our growth strategies, which, in turn, would have an adverse effect on our financial condition, results of operations, cash flows and ability to make expected distributions to our shareholders.

        Our business could be adversely affected by a negative audit by the United States Government.    Agencies of the United States, including the Defense Contract Audit Agency and various agency Inspectors General, routinely audit and investigate government contractors. These agencies review a contractor's performance under its contracts, cost structure and compliance with applicable laws, regulations, and standards. The United States Government also reviews the adequacy of, and a contractor's compliance with, its internal control systems and policies. Any costs found to be misclassified may be subject to repayment. If an audit or investigation uncovers improper or illegal activities, we may be subject to civil or criminal penalties and administrative sanctions, including termination of contracts, forfeiture of profits, suspension of payments, fines, and suspension or prohibition from doing business with the United States Government. In addition, we could suffer serious reputational harm if allegations of impropriety were made against us.

        Our ownership limits are important factors.    Our Declaration of Trust limits ownership of our common shares by any single shareholder to 9.8% of the number of the outstanding common shares or 9.8% of the value of the outstanding common shares, whichever is more restrictive. Our Declaration of Trust also limits ownership by any single shareholder of our common and preferred shares in the aggregate to 9.8% of the aggregate value of the outstanding common and preferred shares. We call these restrictions the "Ownership Limit." Our Declaration of Trust allows our Board of Trustees to exempt shareholders from the Ownership Limit. The Ownership Limit and the restrictions on ownership of our common shares may delay or prevent a transaction or a change of control that might involve a premium price for our common shares or otherwise be in the best interest of our shareholders.

        Our Declaration of Trust includes other provisions that may prevent or delay a change of control.    Subject to the requirements of the New York Stock Exchange, our Board of Trustees has the authority, without shareholder approval, to issue additional securities on terms that could delay or prevent a change in control. In addition, our Board of Trustees has the authority to reclassify any of our unissued common shares into preferred shares. Our Board of Trustees may issue preferred shares with such preferences, rights, powers and restrictions as our Board of Trustees may determine, which could also delay or prevent a change in control.

        The Maryland business statutes also impose potential restrictions on a change of control of our company.    Various Maryland laws may have the effect of discouraging offers to acquire us, even if the acquisition would be advantageous to shareholders. Resolutions adopted by our Board of Trustees and/or provisions of our bylaws exempt us from such laws, but our Board of Trustees can alter its resolutions or change our bylaws at any time to make these provisions applicable to us.

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        Our failure to qualify as a REIT would have adverse tax consequences, which would substantially reduce funds available to make distributions to our shareholders.    We believe that since 1992 we have qualified for taxation as a REIT for Federal income tax purposes. We plan to continue to meet the requirements for taxation as a REIT. Many of these requirements, however, are highly technical and complex. The determination that we are a REIT requires an analysis of various factual matters and circumstances that may not be totally within our control. For example, to qualify as a REIT, at least 95% of our gross income must come from certain sources that are specified in the REIT tax laws. We are also required to distribute to shareholders at least 90% of our REIT taxable income (excluding capital gains). The fact that we hold most of our assets through our Operating Partnership and its subsidiaries further complicates the application of the REIT requirements. Even a technical or inadvertent mistake could jeopardize our REIT status. Furthermore, Congress and the Internal Revenue Service might make changes to the tax laws and regulations and the courts might issue new rulings that make it more difficult or impossible for us to remain qualified as a REIT.

        If we fail to qualify as a REIT, we would be subject to Federal income tax at regular corporate rates. Also, unless the Internal Revenue Service granted us relief under certain statutory provisions, we would remain disqualified as a REIT for four years following the year we first fail to qualify. If we fail to qualify as a REIT, we would have to pay significant income taxes and would therefore have less money available for investments or for distributions to our shareholders. In addition, if we fail to qualify as a REIT, we will no longer be required to pay dividends. As a result of all these factors, our failure to qualify as a REIT could impair our ability to expand our business and raise capital and would likely have a significant adverse effect on the value of our securities.

        We could face possible adverse changes in tax laws, which may result in an increase in our tax liability.    From time to time changes in state and local tax laws or regulations are enacted, which may result in an increase in our tax liability. The shortfall in tax revenues for states and municipalities in recent years may lead to an increase in the frequency and size of such changes. If such changes occur, we may be required to pay additional taxes on our assets or income. These increased tax costs could adversely affect our financial condition and results of operations and the amount of cash available for payment of dividends.

        A number of factors could cause our security prices to decline.    As is the case with any publicly-traded securities, certain factors outside of our control could influence the value of our common and preferred shares. These conditions include, but are not limited to:

•

market perception of REITs in general and office REITs in particular;



•

market perception of REITs relative to other investment opportunities;



•

the level of institutional investor interest in our Company;



•

general economic and business conditions;



•

prevailing interest rates;



•

our financial performance;



•

our underlying asset value;



•

market perception of our financial condition, performance, dividends and growth potential; and



•

adverse changes in tax laws.

        We may experience significant losses and harm to our financial condition if financial institutions holding our cash and cash equivalents file for bankruptcy protection.    We believe that we maintain our cash and cash equivalents with high quality financial institutions. We have not experienced any

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losses to date on our deposited cash. However, we may incur significant losses and harm to our financial condition in the future if any of these financial institutions files for bankruptcy protection.

        Certain of our Trustees have potential conflicts of interest.    Certain members of our Board of Trustees own partnership units in our Operating Partnership. These individuals may have personal interests that conflict with the interests of our shareholders. For example, if our Operating Partnership sells or refinances certain of the properties that these Trustees contributed to the Operating Partnership, the Trustees could suffer adverse tax consequences. Their personal interests could conflict with our interests if such a sale or refinancing would be advantageous to us. We have certain policies in place that are designed to minimize conflicts of interest. We cannot, however, provide assurance that these policies will be successful in eliminating the influence of such conflicts, and if they are not successful, decisions could be made that might fail to reflect fully the interests of all of our shareholders.

        We are dependent on our key personnel, and the loss of any key personnel could have an adverse effect on our operations.    We are dependent on our executive officers. The loss of any of their services could have an adverse effect on our operations. Although certain of our officers have entered into employment agreements with us, we cannot assure you that they will remain employed with us.

        We may change our policies without shareholder approval, which could adversely affect our financial condition, results of operations, market price of our common shares or ability to pay distributions. Our Board of Trustees determines all of our policies, including our investment, financing and distribution policies. Although our Board of Trustees has no current plans to do so, it may amend or revise these policies at any time without a vote of our shareholders. Policy changes could adversely affect our financial condition, results of operations, the market price of our securities or distributions.

Item 1B.    Unresolved Staff Comments

        None

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Item 2.    Properties

        The following table provides certain information about our wholly owned office properties as of December 31, 2009:

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