Exhibit 99.1

OneBeacon Insurance Group, Ltd.

Investor Financial Supplement

March 31, 2011

OneBeacon Insurance Group, Ltd.

Address:

601 Carlson Parkway, Minnetonka, MN 55305 (U.S. Corporate Headquarters)

Internet address:

www.onebeacon.com

Common Stock

Common Stock of OneBeacon Insurance Group, Ltd. is traded on the New York Stock Exchange under the symbol “OB”.

Insurance Financial Strength Ratings

This report is for informational purposes only and should be read in conjunction with documents filed by OneBeacon Insurance Group, Ltd. (the Company) with the U.S. Securities and Exchange Commission, including the Company’s most recent Annual Report on Form 10-K and Quarterly Reports on Form 10-Q.

OneBeacon Insurance Group, Ltd.

Investor Financial Supplement

Table of Contents

OneBeacon Insurance Group, Ltd.

Basis of Presentation

Presentation

·       To better align its operating and reporting structure with the Company’s business profile as a result of the transactions described below, OneBeacon revised its segment structure during the fourth quarter of 2010.  As a result,  financial information included herein reflects results for Specialty Insurance Operations, Other Insurance Operations and Investing, Financing and Corporate Operations. Additionally, as part of the resegmention, agency results for business written on OneBeacon paper and in whch OneBeacon has an ownership interest have been reclassified within the underwriting results.  Financial information for the prior periods has been reclassified to confom to this presentation.

·        Specialty Insurance Operations  is a collection of niche businesses that are aggregated into three major underwriting units for financial reporting: MGA Business, Specialty Industries and Specialty Products.   MGA Business includes Collector Cars and Boats, A.W.G. Dewar and OneBeacon Entertainment.  Specialty Industries includes International Marine Underwriters, OneBeacon Technology Insurance, Specialty Accident and Health, OneBeacon Government Risks and OneBeacon Energy Group.  Specialty Products includes OneBeacon Professional Insurance (which now includes Financial Services), Property and Inland Marine, OneBeacon Specialty Property and OneBeacon Excess and Surplus.

·       Other Insurance Operations includes AutoOne Insurance, a division that offers products and services to assigned risk markets.  Other Insurance Operations also includes the non-specialty Commercial Lines business  that is subject to the renewal rights agreement with The Hanover Insurance Group that began with January 1, 2010 effective dates, the traditional personal lines business  that was subject to the sale  to Tower Group, Inc. completed July 1, 2010, other run-off business and certain purchase accounting adjustments relating to  OneBeacon’s acquisition by White Mountains.

·       Investing, Financing and Corporate Operations includes the investing and financing activities for OneBeacon on a consolidated basis, and certain other activities conducted through  the  top holding company, OneBeacon Insurance Group, Ltd., and its intermediate subsidiaries.

·       The key measure of relative underwriting performance for an insurance company is the combined ratio. An insurance company’s combined ratio under accounting principles generally accepted in the United States of America (“GAAP”) is calculated by adding the ratio of incurred loss and loss adjustment expenses (“LAE”) to earned premiums (the “loss and LAE ratio”) and the ratio of policy acquisition and other underwriting expenses to earned premiums (the “expense ratio”). A combined ratio under 100% indicates that an insurance company is generating an underwriting profit. However, when considering investment income and investment gains or losses, insurance companies operating at a combined ratio of greater than 100% can be profitable.

·        NM - Not meaningful

Non-GAAP Financial Measures

·       This financial supplement includes non-GAAP financial measures that have been reconciled to their most comparable GAAP financial measures.  Management believes these measures to be useful supplements to the comparable GAAP measures in evaluating the Company’s financial performance.

·        Operating income (loss) is a non-GAAP financial measure that excludes net realized and unrealized investment gains (losses) and the related tax effects from net income (loss) attributable to OneBeacon’s common shareholders.  Management believes that this non-GAAP financial measure provides a useful alternative picture of the underlying operating activities of the Company to the GAAP measure of net income (loss) attributable to OneBeacon’s common shareholders, as it removes variability in the timing of investment gains and losses which may be heavily influenced by investment market conditions.  Although key to the Company’s overall financial performance, management believes that realized and unrealized investment gains or losses are largely independent of the underwriting decision-making process. The reconciliation of net income (loss) attributable to OneBeacon’s common shareholders to operating income (loss) is included on page 3.

i

OneBeacon Insurance Group, Ltd.

Basis of Presentation (Continued)

Non-GAAP Financial Measures (continued)

·       Operating income (loss) per share is calculated by dividing operating income (loss) (a non-GAAP financial measure described above) by the weighted average number of common shares outstanding.  Management believes that operating income (loss) per share is a useful alternative picture of the underlying operating activities of the Company as it removes variability in the timing of investment gains and losses which may be heavily influenced by investment market conditions.  Net income (loss) attributable to OneBeacon’s common shareholders per share is the most directly comparable GAAP measure.  As described above, the reconciliation of net income (loss) attributable to OneBeacon’s common shareholders to operating income (loss) is included on page 3. The calculation of operating income (loss) per share is also included on page 3.

·       Adjusted OneBeacon’s common shareholders’ equity excluding cumulative net unrealized investment gains and losses, after tax, and accumulated other comprehensive income (loss) (AOCI/L), the average of which is used in calculating operating returns, is derived by excluding cumulative net unrealized investment gains and losses and net foreign currency gains and losses on investments, after tax, and accumulated other comprehensive income or loss AOCI/L from OneBeacon’s common shareholders’ equity.  For the reasons described above, management believes that it is appropriate to remove the variability in the timing of unrealized investment gains and losses and net foreign currency gains and losses on investments, after tax, and other comprehensive income and loss items when analyzing certain performance measures.  The reconciliation of OneBeacon’s common shareholders’ equity, the most closely comparable GAAP measure, to adjusted OneBeacon’s common shareholders’ equity excluding cumulative net unrealized investment gains and losses, after tax, and AOCI/L, is included on page 4.

·       Combined ratio before catastrophes; combined ratio before catastrophes and prior accident year development; and combined ratio before catastrophes, prior accident year development and long-term incentive compensation (LTIP) expense are non-GAAP financial measures which are derived by excluding catastrophes, prior accident year development and LTIP expense, individually and cumulatively from the GAAP combined ratio.  A catastrophe is a severe loss, resulting from natural or man-made events, including risks such as fire, earthquake, windstorm, explosion, terrorism or other similar events. Each catastrophe has unique characteristics. Catastrophes are not predictable as to timing or loss amount in advance. Development on prior accident year losses generally results from changes in facts or events about the underlying loss or related loss adjustment expenses from that known and judgments made at the time the loss was incurred. Similar to catastrophe losses, development on prior accident year losses is not predictable.  OneBeacon expenses the full cost of all of its long-term incentive compensation.  OneBeacon believes that a discussion of the effect of catastrophes, prior accident year development and LTIP expense on the GAAP combined ratio is meaningful for investors to understand the variability of periodic earnings. The reconciliation of these non-GAAP financial measures to the GAAP combined ratio, the most closely comparable GAAP measure, is found on pages 7, 10, 11, 12, 13, 14 and 15.

·       Pre-tax operating income before interest expense on debt is a non-GAAP financial measure that excludes net realized and unrealized investment gains and losses as well as interest expense on debt from pre-tax income.  Management believes that pre-tax operating income before interest expense on debt provides a useful alternative picture of the underlying operating activities of the Company to the GAAP measure of pre-tax income, as it removes variability in the timing of investment gains and losses which may be heavily influenced by investment market conditions.  Although key to the Company’s overall financial performance, management believes that realized and unrealized investment gains or losses are largely independent of the underwriting decision-making process. The reconciliation of pre-tax income to pre-tax operating income before interest expense on debt is included on page 21.

·       Interest coverage is calculated by dividing adjusted pre-tax operating income before interest expense on debt (a non-GAAP financial measure described above) by interest expense on debt.  Management believes that interest coverage is a useful supplement to understanding the Company’s capital position.  The reconciliation of the numerator to the most closely comparable GAAP measure is described above.  The calculation of interest coverage is included on page 21.

ii

OneBeacon Insurance Group, Ltd.

Safe Harbor Statement

Forward-looking statements contained in this presentation are based on the Company’s assumptions and expectations concerning future events and financial performance and are made pursuant to the safe harbor provisions of the Private Securities Litigation Reform Act of 1995. Such statements are subject to significant business, economic and competitive risks and uncertainties that could cause actual results to differ materially from those reflected in the forward-looking statements. OneBeacon’s forward-looking statements could be affected by numerous foreseeable and unforeseeable events and developments such as exposure to catastrophe, or other large property and casualty losses, adequacy of reserves, risks associated with implementing business strategies, levels and pricing of new and renewal business achieved, credit, interest, currency and other risks associated with the Company’s investment portfolio, changes in accounting policies, and other factors identified in the Company’s Forms 10-Q and 10-K filed with the Securities and Exchange Commission. In light of the significant uncertainties inherent in the forward-looking information contained herein, readers are cautioned not to place undue reliance on these forward-looking statements, which speak only as of the dates on which they are made. The Company disclaims any obligation to publicly update or revise any forward-looking information or statements.

iii

OneBeacon Insurance Group, Ltd.

Consolidated Financial Results

(in millions, except per share amounts)

[1]     Internal rate of return (IRR) calculated based on beginning book value per share, dividends paid and ending book value per share.  Includes a quarterly dividend of $0.21 per share.

[2]     Internal rate of return (IRR) calculated based on beginning book value per share, dividends paid and ending book value per share.  Includes dividends of $0.84 per share (a quarterly dividend of $0.21 per share) and a special dividend of $2.50 per share paid in September 2010.

[3]     Includes the impact of repurchases of Class A common shares made through the Company’s share repurchase program.

1

OneBeacon Insurance Group, Ltd.

Consolidated Statements of Operations and Comprehensive Income

($ in millions)

2

OneBeacon Insurance Group, Ltd.

Comprehensive Income, Net Income and Operating Income (Loss)

(in millions, except per share amounts)

[1] Includes the impact of repurchases of Class A common shares made through the Company’s share repurchase program.

3

OneBeacon Insurance Group, Ltd.

Computation of Return on Equity Measures

($ in millions)

4

OneBeacon Insurance Group, Ltd.

Consolidated Balance Sheets

As of December 31, 2010 and March 31, 2011

($ in millions)

[1] In connection with purchase accounting for the OneBeacon Acquisition, OneBeacon was required to adjust to fair value its loss and LAE reserves and the related reinsurance recoverables on the acquired balance sheet. This adjustment is being accreted ratably with and over the period the claims are settled. As of December 31, 2010 and March 31, 2011, the balances of these purchase accounting adjustments were $176.5 and $173.2, respectively.

5

OneBeacon Insurance Group, Ltd.

Book Value Per Share

(in millions, except per share amounts)

[1] Includes the impact of repurchases of Class A common shares made through the Company’s share repurchase program.

6

OneBeacon Insurance Group, Ltd.

Consolidated Pre-Tax Results from Operations

($ in millions)