Exhibit 99.1

NEWS RELEASE TRANSMITTED BY Business Wire

FOR:                                   ATLANTIC POWER CORPORATION

SYMBOL:                          NYSE: AT; TSX: ATP

May 11, 2011

Atlantic Power Corporation Releases First Quarter 2011 Results

BOSTON, MASSACHUSETTS — Atlantic Power Corporation (NYSE: AT) (TSX: ATP) (“Atlantic Power” or the “Company”) today announced its results for the quarter ended March 31, 2011.  All amounts are in U.S. dollars unless otherwise indicated.  Please see “Regulation G Disclosures” attached to this news release for an explanation and US GAAP reconciliation of the terms “EBITDA”, “Adjusted EBITDA” and “Cash Available for Distribution” as used in this news release.

Highlights

·                  Operating results in line with annual guidance

·                  Construction at Piedmont Green Power is on schedule and on budget

·                  Closed sale of Topsham project for cash proceeds of $8.5 million

·                  Maintaining guidance to sustain current level of dividends into 2016, even with no positive impact from potential acquisitions or organic growth

“Our results for the quarter met our expectations and are in line with our guidance for the year,” commented Barry Welch, President and CEO.  “We continue to focus on accretive acquisition opportunities to enhance our long-term cash flows and are confident that we can continue to execute on our growth strategy.”

Operating Performance

Project Adjusted EBITDA, including earnings from equity investments, decreased by $2.8 million to $36.0 million for the quarter ended March 31, 2011 compared to $38.8 million for the same period last year. The decrease was primarily attributable to maintenance at three of our projects, which was partially offset by an increase in EBITDA from acquisitions as well as from favorable energy prices at Lake and Auburndale. Project Adjusted EBITDA in the first quarter was affected by the following factors:

·                  EBITDA of $1.7 million at Cadillac, as the project was acquired in December 2010;

·                  increased EBITDA of $2.1 million at Lake and Auburndale due to increased contractual capacity payments under the project’s PPA and favorable energy prices; offset by

·                  decreased EBITDA of $2.5 million at Pasco primarily attributable to higher operations and maintenance expenses related to the unplanned replacement of gas turbine blades during a maintenance outage;

·                  decreased EBITDA of $2.4 million at Selkirk primarily attributable to lower capacity revenue.  A planned outage was longer than expected resulting in a delay in the receipt of capacity payments until the second quarter; and

·                  decreased EBITDA of $1.3 million at Chambers attributable to higher maintenance costs associated with a planned outage in April and lower dispatch during the first quarter.

Cash Flow Available for Distribution

For the three months ended March 31, 2011, Cash Flow Available for Distribution decreased by $1.2 million compared to the same period last year.  Our payout ratio for the first quarter 2011 was 114% as compared to 89% in the same period in 2010.  The increase in our payout ratio is primarily attributable to the increased dividend obligation from our common share issuance in October of 2010.  Our current payout ratio and project distributions are in line with our expectations and previous guidance for the full year 2011.

Construction of Piedmont Green Power

The construction of Piedmont Green Power, our 53 MW biomass project, is on schedule and on budget and the remainder of our equity has been contributed, bringing our total equity investment to $75 million.  The remainder of the construction costs will be funded by the project-level financing that was closed in October 2010.  Turnkey construction of the project is led by Zachry Industrial and we are managing construction risks jointly with our affiliate, Rollcast Energy.  Cash distributions to the Company from the project are expected to average $8 million to $10 million for each full year of project operation after completion of construction in late 2012.

Sale of Topsham

On February 28, 2011, we entered into a purchase and sale agreement with an affiliate of ArcLight Capital Partners, LLC for the purchase of our lessor interest in the project.  The transaction closed on May 6, 2011 and we received cash proceeds of $8.5 million, resulting in no gain or loss on the sale.

Guidance

Based on actual performance to date and projections for the remainder of the year, we confirm our previous guidance that we expect to receive distributions from our projects in the range of $80 million to $90 million for the full year 2011 compared to $83 million in 2010.  We continue to expect overall levels of operating cash flows in 2011 to be improved over actual 2010 levels. Higher distributions from existing projects, initial distributions from our recent investments in Idaho Wind and Cadillac, and a slightly lower payment under the management termination agreement are expected to be partially offset by the non-recurrence of the cash tax refunds received in 2010. These increased operating cash flows in 2011, combined with the impact of our recent public offerings, are expected to result in a payout ratio of approximately 100% to 105% in 2011 subject to the financial performance of our projects for the balance of the year.  In 2012, additional increases in distributions from projects are expected to further increase operating cash flow compared to 2011, the most significant factor being increased distributions from Selkirk following the final payment of its non-recourse project level debt in mid-2012.

Based on management’s cash flow projections, we believe the current level of dividends is sustainable into 2016 before considering any positive impacts from potential future acquisitions or organic growth opportunities.

Outstanding Common Shares and Convertible Debentures

As of May 10, 2011, we had 68,531,901 common shares, Cdn$48.1 million principal amount of 6.50% convertible secured debentures due October 31, 2014, Cdn$75.0 million principal amount of 6.25% convertible debentures due March 15, 2017, and Cdn$80.5 million principal amount of 5.60% convertible debentures due June 30, 2017 outstanding. Holders of common shares currently receive a monthly dividend at an annual rate of Cdn$1.094 per common share.

The calculation of Cash Available for Distribution and a summary of Adjusted EBITDA by individual project for the quarter ended March 31, 2011 are attached to this news release.

Copies of financial data and other publicly filed documents, including the Company’s annual information form, are available on SEDAR at www.sedar.com under “Atlantic Power Corporation” or on the Company’s website at www.atlanticpower.com.

Investor Conference Call and Webcast

A telephone conference call hosted by Atlantic Power’s management team will be held on Thursday, May 12, 2011 at 10:00 AM ET.  The telephone numbers for the conference call are: Local/International: (416) 849-2698, North American Toll Free: (866) 400-2270.  The Conference Call will also be broadcast over Atlantic Power’s website at www.atlanticpower.com. Please call or log in 10 minutes prior to the call. The telephone numbers to listen to the conference call after it is completed (Instant Replay) are Local/International: (416) 915-1035, North American Toll Free (866) 245-6755. Please enter the passcode 377980# when instructed. The conference call will also be archived on Atlantic Power’s web site.

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About Atlantic Power

Atlantic Power Corporation owns and operates a diverse fleet of power generation and infrastructure assets in the United States.  Our power generation projects sell electricity to utilities and other large commercial customers under long-term power purchase agreements, which seek to minimize exposure to changes in commodity prices.  Our power generation projects in operation have an aggregate gross electric generation capacity of approximately 1,948 megawatts in which our ownership interest is approximately 871 MW.  Our corporate strategy is to generate stable cash flows from our existing assets and to make accretive acquisitions to sustain our dividend payout to shareholders, which is currently paid monthly at an annual rate of Cdn$1.094 per share.   Our current portfolio consists of interests in 12 operational power generation projects across nine states, one biomass project under construction in Georgia, and an 84-mile,500 kilovolt electric transmission line located in California.  Atlantic Power also owns a majority interest in Rollcast Energy, a biomass power plant developer with several projects under development.

Atlantic Power trades on the New York Stock Exchange under the symbol AT, on the Toronto Stock Exchange under the symbol ATP and has a market capitalization of approximately $1.0 billion.  For more information, please visit the Company’s website at www.atlanticpower.com or contact:

Atlantic Power Corporation

Patrick Welch, Chief Financial Officer

(617) 977-2700

info@atlanticpower.com

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Forward-looking Statements

Certain statements in this news release may constitute “forward-looking statements”, which reflect the expectations of management regarding the future growth, results of operations, performance and business prospects and opportunities of our Company and our projects.  These statements, which are based on certain assumptions and describe our future plans, strategies and expectations, can generally be identified by the use of the words “may,” “will,” “project,” “continue,” “believe,” “intend,” “anticipate,” “expect” or similar expressions that are predictions of or indicate future events or trends and which do not relate solely to present or historical matters.  Examples of such statements in this press release include, but are not limited, to statements with respect to the following:

·                  The belief that, based on management’s cash flow projections, the current level of dividends is sustainable into 2016 without additional acquisitions or organic growth opportunities;

·                  The expectation that distributions from our projects will be in the range of $80 million to $90 million for the full year 2011;

·                  The expectation that overall levels of operating cash flows in 2011 will be improved over actual 2010 levels;

·                  The expectation that the payout ratio in 2011 will be approximately 100%-105% and that improvements in cash flow and payout ratio are expected in 2012;

·                  The expectation that cash distributions from Piedmont are expected to average $8 million to $10 million for each full year of project operation; and

·                  The expectation that Piedmont will complete construction in late 2012.

Forward-looking statements involve significant risks and uncertainties, should not be read as guarantees of future performance or results, and will not necessarily be accurate indications of whether or not or the times at or by which such performance or results will be achieved.  Please refer to the factors discussed under “Risk Factors” in the Company’s periodic reports as filed with the Securities and Exchange Commission from time to time for a detailed discussion of the risks and uncertainties affecting our Company.  Although the forward-looking statements contained in this news release are based upon what are believed to be reasonable assumptions, investors cannot be assured that actual results will be consistent with these forward-looking statements, and the differences may be material.  These forward-looking statements are made as of the date of this news release and, except as expressly required by applicable law, the Company assumes no obligation to update or revise them to reflect new events or circumstances.  The financial outlook information contained in this news release is presented to provide readers with guidance on the cash distributions expected to be received by the Company and to give readers a better understanding of the Company’s ability to pay its current level of distributions into the future.  Readers are cautioned that such information may not be appropriate for other purposes.

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Atlantic Power Corporation

Consolidated Balance Sheets (in thousands of U.S. dollars)

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Atlantic Power Corporation

Consolidated Statements of Operations (in thousands of U.S. dollars)

(Unaudited)

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Atlantic Power Corporation

Consolidated Statements of Cash Flows (in thousands of U.S. dollars)

(Unaudited)

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Regulation G Disclosures

Cash Available for Distribution is not a measure recognized under U.S. generally accepted accounting principles (“GAAP”) and does not have a standardized meaning prescribed by GAAP.  Management believes Cash Available for Distribution is a relevant supplemental measure of the Company’s ability to earn and distribute cash returns to investors.  A reconciliation of Cash Flows from Operating Activities to Cash Available for Distributions is provided below.  Investors are cautioned that the Company may calculate this measure in a manner that is different from other companies.

Adjusted EBITDA, earnings before interest, taxes, depreciation and amortization (including non-cash impairment charges), is not a measure recognized under GAAP and is therefore unlikely to be comparable to similar measures presented by other issuers and does not have a standardized meaning prescribed by GAAP.  Management uses Adjusted EBITDA at the Project-level to provide comparative information about project performance.  A reconciliation of Project Adjusted EBITDA to project income is provided on the following page.  Investors are cautioned that the Company may calculate this measure in a manner that is different from other issuers.

Atlantic Power Corporation

Cash Available for Distribution

(In thousands of U.S. dollars, except as otherwise stated)

(Unaudited)

(1)                      Excludes construction-in-progress costs related to our Piedmont biomass project.

(2)                     Cash Available for Distribution is not a recognized measure under GAAP and does not have any standardized meaning prescribed by GAAP. Therefore, this measure may not be comparable to similar measures presented by other companies.

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Atlantic Power Corporation

Project Adjusted EBITDA (in thousands of U.S. dollars)

(Unaudited)

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