Exhibit (a)(1)(G) THIS ANNOUNCEMENT IS NEITHER AN OFFER TO PURCHASE NOR A SOLICITATION OF AN OFFER TO SELL SHARES. THE OFFER IS MADE SOLELY BY THE OFFER TO PURCHASE DATED AUGUST 21, 2000 AND THE RELATED LETTER OF TRANSMITTAL, AND IS NOT BEING MADE TO (NOR WILL TENDERS BE ACCEPTED FROM OR ON BEHALF OF) HOLDERS OF SHARES RESIDING IN ANY JURISDICTION IN WHICH THE MAKING OF THE OFFER OR THE ACCEPTANCE THEREOF WOULD NOT BE IN COMPLIANCE WITH THE LAWS OF SUCH JURISDICTION. NOTICE OF OFFER TO PURCHASE FOR CASH BY WHITE MOUNTAINS INSURANCE GROUP, LTD. UP TO 1,500,000 OF ITS COMMON SHARES AT $165.00 NET PER SHARE White Mountains Insurance Group, Ltd., a company organized under the laws of Bermuda (the "Company"), is inviting its shareholders to tender its Common Shares, par value $1.00 per share ("Shares"), to the Company, at $165.00 per Share, net to the seller in cash, upon the terms and subject to the conditions set forth in the Offer to Purchase dated August 21, 2000 (the "Offer to Purchase"), and in the related Letter of Transmittal (which together constitute the "Offer"). For purposes of the Offer, the Company shall be deemed to have accepted for payment (and thereby purchased), subject to proration, Shares which are tendered and not withdrawn when, as and if the Company gives oral or written notice to the Depositary of the Company's acceptance of such Shares for payment pursuant to the Offer. The Company reserves the right, in its sole discretion, to purchase more than 1,500,000 Shares pursuant to the Offer. THE OFFER IS NOT CONDITIONED UPON ANY MINIMUM NUMBER OF SHARES BEING TENDERED. THE OFFER IS, HOWEVER, SUBJECT TO CERTAIN OTHER CONDITIONS. SEE SECTION 12 OF THE OFFER TO PURCHASE. - -------------------------------------------------------------------------------- THE OFFER, PRORATION PERIOD AND WITHDRAWAL RIGHTS WILL EXPIRE AT 12:00 MIDNIGHT, NEW YORK CITY TIME, ON MONDAY, SEPTEMBER 18, 2000, UNLESS THE OFFER IS EXTENDED. - -------------------------------------------------------------------------------- NEITHER THE COMPANY NOR ITS BOARD OF DIRECTORS MAKES ANY RECOMMENDATION AS TO WHETHER ANY SHAREHOLDER SHOULD TENDER ANY OR ALL OF SUCH SHAREHOLDER'S SHARES PURSUANT TO THE OFFER. EACH SHAREHOLDER MUST MAKE SUCH SHAREHOLDER'S OWN DECISION WHETHER TO TENDER SHARES AND, IF SO, HOW MANY SHARES TO TENDER. The Company reserves the right, in its sole discretion, at any time or from time to time, to extend the period of time during which the Offer is open by giving oral or written notice of such extension to the Depositary and making a public announcement thereof. See Section 1 of the Offer to Purchase. If the number of Shares properly tendered and not withdrawn before 12:00 midnight, New York City time, on Monday, September 18, 2000, or the latest time and date at which the Offer, if extended by the Company, shall expire (the "Expiration Date"), is greater than 1,500,000 Shares (or such greater number of Shares as the Company may elect to purchase pursuant to the Offer), the Company, upon the terms and subject to the conditions of the Offer, will accept Shares for purchase in the following order of priority: (a) first, all Shares properly tendered and not withdrawn before the Expiration Date by any shareholder who beneficially owned as of the close of business on August 14, 2000, and who continues to own beneficially until the Expiration Date an aggregate of fewer than 100 Shares and who: (1) tenders all Shares beneficially owned by such shareholder (partial tenders will not qualify for this preference), and (2) completes the box captioned "Odd Lots" on the Letter of Transmittal and, if applicable, on the Notice of Guaranteed Delivery; and (b) then, after purchase of all the foregoing Shares, all other Shares properly tendered and not withdrawn before the Expiration Date on a pro rata basis, if necessary (with adjustments to avoid purchases of fractional Shares). Except as otherwise provided in Section 4 of the Offer to Purchase, a tender of Shares pursuant to the Offer is irrevocable. Shares tendered pursuant to the Offer may be withdrawn at any time before the Expiration Date and, unless theretofore accepted for payment by the Company, after 12:00 midnight, New York City time, on Tuesday, October 17, 2000. See Section 4 of the Offer to Purchase. For a withdrawal to be effective, the Depositary must timely receive (at one of its addresses set forth on the back cover of the Offer to Purchase) a written or facsimile transmission notice of withdrawal. Any notice of withdrawal must specify the name of the person having tendered the Shares to be withdrawn, the number of Shares to be withdrawn and, if different from the name of the person who tendered the Shares, the name of the registered owner of such Shares. If the certificates have been delivered or otherwise identified to the Depositary, then, prior to the release of such certificates, the tendering shareholder must also submit the serial numbers shown on the particular certificates evidencing such Shares and the signature on the notice of withdrawal must be guaranteed by an Eligible Institution (as defined in Section 3 of the Offer to Purchase) (except in the case of Shares tendered by an Eligible Institution). If Shares have been delivered pursuant to the procedure for book-entry transfer set forth in Section 3 of the Offer to Purchase, the notice of withdrawal must specify the name and number of the account at The Depository Trust Company (as defined in Section 2 of the Offer to Purchase) to be credited with the withdrawn Shares and otherwise comply with the procedures of such facility. A withdrawal of a tender of Shares may not be rescinded and Shares properly withdrawn shall thereafter be deemed to be not validly tendered for purposes of the Offer. Withdrawn Shares, however, may be retendered before the Expiration Date by again following any of the procedures described in Section 3 of the Offer to Purchase. THE OFFER TO PURCHASE AND THE LETTER OF TRANSMITTAL CONTAIN IMPORTANT INFORMATION THAT SHOULD BE READ BEFORE ANY DECISION IS MADE WITH RESPECT TO THE OFFER. These documents are being mailed to record holders of Shares and will be furnished to brokers, dealers, commercial banks, trust companies and similar persons whose names, or the names of whose nominees, appear on the Company's shareholder list or, if applicable, who are listed as participants in a clearing agency's security position listing for subsequent transmittal to beneficial owners of Shares. The information required to be disclosed by Rule 13e-4(d)(1) of the General Rules and Regulations under the Securities Exchange Act of 1934 is contained in the Offer to Purchase and is incorporated herein by reference. Any questions or requests for assistance may be directed to the Information Agent at its address and telephone number set forth below. Requests for copies of the Offer to Purchase, Letter of Transmittal, Notice of Guaranteed Delivery or other tender offer materials may be directed to the Information Agent and such copies will be furnished promptly at the Company's expense. Shareholders may also contact their broker, dealer, commercial bank, trust company or other nominee for assistance concerning the Offer. THE DEPOSITARY AND THE INFORMATION AGENT FOR THE OFFER IS: EQUISERVE TRUST COMPANY BY MAIL: BY FEDERAL EXPRESS OR OTHER BY HAND: COURIER: Equiserve Trust Company Equiserve Trust Company Equiserve Trust Company P.O. Box 842010 40 Campanelli Drive c/o Securities Transfer and Boston, MA 02284-2010 Braintree, MA 02184 Reporting Services, Inc. Attention: White Mountains Attn: Corporate Actions 100 William Street, Galleria 1-888-756-1854 New York, NY 10038 August 21, 2000