OneBeacon Insurance Group's US operating companies have been affirmed the financial strength rating (FSR) of A (excellent) and the issuer credit ratings (ICR) of "a" and Esurance Insurance Group's US operating companies have been affirmed the FSR of A- (excellent) and ICRs of "a-" by AM Best Co.

Concurrently, Best has affirmed the ICR of "bbb" of OneBeacon's publicly-traded parent, OneBeacon Insurance Group Ltd. and its intermediated holding company, OneBeacon US Holdings Inc.

Additionally, Best has affirmed the FSR of A- (excellent) and ICR of "a-" of White Mountains Reinsurance Company of America and the ICR of "bbb-" as well as the debt ratings of its intermediate parent holding company, White Mountains Re Group Ltd.

The ratings agency also has affirmed the ICR of "bbb" and debt ratings of the group's ultimate parent, White Mountains Insurance Group Ltd. The outlook for all ratings is stable. Best said that White Mountains' ratings reflected its strong financial flexibility and the solid operating results generated through its operating subsidiaries.

OneBeacon's ratings reflect its sound risk-adjusted capitalisation and strong earnings through its favourable underwriting and operating performance, said Best. The ratings also consider the financial flexibility of OneBeacon US and OneBeacon Ltd. These positive rating factors were partially offset by OneBeacon's weak underwriting and operating performance prior to 2003, largely related to adverse development on its run-off operations.

Esurance's ratings recognise its solid risk-adjusted capitalisation and the ongoing support of White Mountains. Offsetting these positive rating factors is the group's high rate of premium growth, significant reinsurance dependence and continued underwriting losses, which generate weak operating results relative to its personal auto peers.