Exhibit 99.1

ONEBEACON REPORTS $11.93 BOOK VALUE PER SHARE

HAMILTON, Bermuda (April 27, 2012) — OneBeacon Insurance Group, Ltd. (NYSE: OB) today reported book value per share of $11.93, an increase of 5.0% for the first quarter, including dividends.

Said Mike Miller, CEO of OneBeacon, “We had a strong start to the year, reflecting excellent Specialty underwriting results and solid investment returns, partially offset by increased reserves in runoff. Our Specialty written premiums grew by 17% to $303 million, and we were pleased to see continued pricing momentum, along with favorable retention and new business trends.  During the quarter we launched our newest specialty business—OneBeacon Program Group—and we closed the previously announced sale of AutoOne. We are optimistic about improving market conditions and will continue to look for new specialty opportunities.”

For the first quarter, comprehensive income and net income were both $44 million, and operating income was $25 million, or $0.26 per share. Operating income is a non-GAAP financial measure which is explained later in this release.

In January 2012, OneBeacon completed the sale of its subsidiary, OneBeacon Holdings (Luxembourg) S.à r.l., to a subsidiary of White Mountains.  As a result of completing the sale,

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OneBeacon recorded a $14 million gain as additional paid in capital, increasing OneBeacon’s book value per share by $0.14.

Insurance Operations: The first quarter GAAP combined ratio was 93.6%, compared to 93.3% for the first quarter of 2011. Specialty Insurance Operations’ GAAP combined ratio was 89.1% compared to 94.3% for the first quarter of last year, reflecting improved current accident year results. The first quarter of 2012 included 4 points of unfavorable loss reserve development compared to 2 points of favorable loss reserve development in the first quarter of last year. The loss reserve development in the current period was driven by 5 points of unfavorable development in the runoff business, including the impact of an adverse court ruling in Mississippi regarding a disputed assessment from an involuntary pool for Hurricane Katrina claims in 2005.

First quarter net written premiums for Specialty Insurance Operations were $303 million as compared to $258 million for the first quarter of 2011. This 17% increase reflects growth across the company’s business units, with particularly strong contributions from OneBeacon Professional Insurance, OneBeacon Technology Insurance and OneBeacon Accident Group.

Consolidated Investment Results:  OneBeacon’s first quarter total return on invested assets was 1.7% compared to 1.4% for the first quarter of 2011. These results included net realized and unrealized investment gains of $30 million and net investment income of $15 million, compared to net realized and unrealized investment gains of $23 million and net investment income of $21 million for the first quarter of 2011. The average market value of invested assets was $2.7 billion in the first quarter as compared to $3.2 billion in the first quarter of 2011, reflecting the impact of the company’s capital management activities.

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Company to Host Webcast:  OneBeacon will host its first quarter 2012 webcast for analysts and investors at 10:00 a.m. ET on Friday, April 27. A copy of the earnings release, the slide presentation to be referenced during the call and a financial supplement are available on the company’s website: www.onebeacon.com. An audio playback of the teleconference will be available on the website shortly following the webcast.

About OneBeacon: OneBeacon Insurance Group, Ltd. is a Bermuda-domiciled holding company that is publicly traded on the New York Stock Exchange under the symbol “OB.” OneBeacon’s underwriting companies offer a range of specialty insurance products sold through independent agencies, regional and national brokers, wholesalers and managing general agencies. Each business is managed by an experienced team of specialty insurance professionals focused on a specific customer group or industry segment. OneBeacon’s solutions target professional liability; ocean and inland marine; collector cars and boats; energy; entertainment, sports and leisure; excess property; environmental; group accident; programs; public entities; technology; and tuition refund. For further information about our products and services visit: www.onebeacon.com and to remain up to date on OneBeacon’s news, follow us on Twitter @OneBeaconIns or visit our online newsroom: www.onebeacon.com/newsroom.

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ONEBEACON INSURANCE GROUP, LTD.

CONSOLIDATED BALANCE SHEETS

($ in millions)

(Unaudited)

(1)          Represents assets and liabilities being sold as part of the AutoOne Transaction required to be presented separately in the December 31, 2011 consolidated balance sheet. The AutoOne Transaction closed on February 22, 2012.

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ONEBEACON INSURANCE GROUP, LTD.

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME

(in millions, except per share amounts)

(Unaudited)

(1)          Results for AutoOne are reported as discontinued operations for all periods presented.

(2)          Weighted average common shares outstanding includes the impact of unvested restricted shares and also the impact of repurchases of Class A common shares made through the company’s share repurchase program.

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ONEBEACON INSURANCE GROUP, LTD.

SEGMENT STATEMENTS OF OPERATIONS

($ in millions)

(Unaudited)

For the Three Months Ended March 31, 2012

For the Three Months Ended March 31, 2011

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ONEBEACON INSURANCE GROUP, LTD.

SUMMARY OF RATIOS AND PREMIUMS

($ in millions)

(Unaudited)

Three Months Ended March 31, 2012

Three Months Ended March 31, 2011

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ONEBEACON INSURANCE GROUP, LTD.

BOOK VALUE PER SHARE

(in millions, except per share amounts)

(Unaudited)

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ONEBEACON INSURANCE GROUP, LTD.

COMPREHENSIVE INCOME, NET INCOME AND OPERATING INCOME

(in millions, except per share amounts)

(Unaudited)

(1) Weighted average common shares outstanding includes the impact of unvested restricted shares and also the impact of repurchases of Class A common shares made through the company’s share repurchase program.

(2) Represents a non-GAAP financial measure. See discussion of Non-GAAP financial measures which begins on page 11.

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ONEBEACON INSURANCE GROUP, LTD.

COMPREHENSIVE AND OPERATING RETURNS ON AVERAGE EQUITY

($ in millions)

(Unaudited)

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Discussion of Non-GAAP Financial Measures

This earnings release includes non-GAAP financial measures that have been reconciled to their most comparable GAAP financial measures.  OneBeacon believes these measures to be useful supplements to the comparable GAAP measures in evaluating OneBeacon’s financial performance.

Operating income is a non-GAAP financial measure that excludes net realized and unrealized investment gains or losses and the related tax effects from net income attributable to OneBeacon’s common shareholders.  OneBeacon 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 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, OneBeacon believes that net realized and unrealized investment gains or losses are largely independent of the underwriting decision-making process. The reconciliation of net income attributable to OneBeacon’s common shareholders to operating income is included on page 9.

Operating income per share is calculated by dividing operating income (a non-GAAP financial measure described above) by the weighted average number of common shares outstanding.  Management believes that operating income 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 attributable to OneBeacon’s common shareholders per share is the most directly comparable GAAP measure.  As described above, the reconciliation of net income attributable to OneBeacon’s common shareholders to operating income is included on page 9. The calculation of operating income per share is also included on page 9.

Adjusted OneBeacon’s common shareholders’ equity excluding 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 net unrealized gains and losses and net foreign currency gains and losses on investments, after tax, and accumulated other comprehensive income or loss (AOCI/L), after tax, from OneBeacon’s common shareholders’ equity. For the reasons described above, OneBeacon believes that it is appropriate to remove the variability in net unrealized gains and losses and net foreign currency gains and losses on investments 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 net unrealized investment gains and losses, after-tax, and AOCI/L, after tax, is included on page 10.

Safe Harbor Statement under the Private Securities Litigation Reform Act of 1995

This press release may contain “forward-looking statements” within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934. All statements, other than statements of historical facts, included or referenced in this release which address activities, events or developments which we expect or anticipate will or may occur in the future are forward-looking statements. The words “will,” “believe,” “intend,” “expect,” “anticipate,” “project,” “estimate,” “predict” and similar expressions are also intended to identify forward-looking statements. These forward-looking statements include, among others, statements with respect to OneBeacon’s:

·      change in book value per share or return on equity;

·      business strategy;

·      financial and operating targets or plans;

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·                  incurred loss and loss adjustment expenses and the adequacy of its loss and loss adjustment expense reserves and related reinsurance;

·                  projections of revenues, income (or loss), earnings (or loss) per share, dividends, market share or other financial forecasts;

·      expansion and growth of our business and operations; and

·      future capital expenditures.

These statements are based on certain assumptions and analyses made by OneBeacon in light of its experience and perception of historical trends, current conditions and expected future developments, as well as other factors believed to be appropriate in the circumstances. However, whether actual results and developments will conform to our expectations and predictions is subject to a number of risks and uncertainties that could cause actual results to differ materially from expectations, including:

·                  claims arising from catastrophic events, such as hurricanes, windstorms, earthquakes, floods, or terrorist attacks;

·                  recorded loss and loss adjustment expense reserves subsequently proving to have been inadequate;

·                  the continued availability and cost of reinsurance coverage;

·                  the continued availability of capital and financing;

·                  general economic, market or business conditions;

·                  business opportunities (or lack thereof) that may be presented to it and pursued;

·                  competitive forces, including the conduct of other property and casualty insurers and agents;

·                  changes in domestic or foreign laws or regulations, or their interpretation, applicable to OneBeacon, its competitors, its agents or its customers;

·                  an economic downturn or other economic conditions adversely affecting its financial position including stock market volatility;

·                  actions taken by ratings agencies from time to time, such as financial strength or credit ratings downgrades or placing ratings on negative watch;

·                  the risks that are described from time to time in OneBeacon’s filings with the Securities and Exchange Commission, including but not limited to OneBeacon’s Annual Report on the Form 10-K for the fiscal year ended December 31, 2011 filed February 28, 2012.

Consequently, all of the forward-looking statements made in this press release are qualified by these cautionary statements, and there can be no assurance that the actual results or developments anticipated by OneBeacon will be realized or, even if substantially realized, that they will have the expected consequences to, or effects on, OneBeacon or its business or operations. OneBeacon assumes no obligation to update publicly any such forward-looking statements, whether as a result of new information, future events or otherwise.

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