White Mountains to Commence Self-Tender Offer to Purchase up to 300,000 of Its Common Shares

Hamilton, Bermuda – 17 August, 2011 - White Mountains Insurance Group, Ltd. (Tickers: NYSE –  WTM; BSX – WTM.BH) today announced that it intends to commence a "modified Dutch auction" self-tender offer to purchase up to 300,000 of its common shares at a purchase price of not greater than $435 or less than $385 per share net to the seller in cash. The tender offer is expected to commence on August 18, 2011 and expire at 12:00 midnight, New York City time, on September 15, 2011, unless extended. White Mountains' common shares closed on the New York Stock Exchange at $403.00 per share on August 16, 2011.

A "modified Dutch auction" self-tender offer allows shareholders to indicate how many shares and at what price within the Company's specified range they wish to tender their shares. Based on the number of shares tendered and the prices specified by the tendering shareholders, the Company will determine the lowest price per share within the range that will enable it to purchase 300,000 shares, or such lesser number of shares that are properly tendered and not properly withdrawn. All shares purchased by the Company in the tender offer will be purchased at the same price regardless of whether the shareholder tendered at a lower price. The Company will not purchase shares below a price stipulated by a shareholder, and in some cases, may actually purchase shares at a price above a shareholder's indication under the terms of the tender offer.

The tender offer will not be conditioned upon any minimum number of shares being tendered. The tender offer will be, however, subject to certain conditions as will be specified in the offer to purchase. Specific instructions and a complete explanation of the terms and conditions of the tender offer will be contained in the offer to purchase, the letter of transmittal and the related materials, which will be mailed to shareholders of record shortly after commencement of the tender offer.

Neither the Company nor its Board of Directors makes any recommendation as to whether any shareholder should participate in the tender offer or as to the price or prices at which shareholders may choose to tender their shares in the tender offer. The Company's directors and executive officers have advised the Company that they do not intend to tender any of their shares in the tender offer.

D.F. King & Co., Inc. will serve as information agent for the tender offer. Shareholders with questions, or who would like to receive additional copies of the tender offer documents when they are available, may call D.F. King & Co., Inc. at (800) 967-4607 (toll free).

ADDITIONAL INFORMATION

White Mountains is a Bermuda-domiciled financial services holding company traded on the New York Stock Exchange and the Bermuda Stock Exchange under the symbol WTM. Additional financial information and other items of interest are available at the Company's web site located at www.whitemountains.com  

CONTACTS:

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