Several insurers and reinsurers are exposed to claims from the loss of the Deepwater Horizon oil drilling rig.

ACE Ltd., AXIS Capital Holdings Ltd. and Lancashire Holdings Ltd. are believed to have “very significant exposures on a direct basis,” one energy market source said.

A spokesman for Zurich-based ACE would not comment on whether the insurer writes coverage for Transocean or others associated with the risk. A spokesman for Bermuda's Lancashire confirmed it is on the risk but would not provide specifics.

AXIS President and CEO John Charman confirmed in a conference call with analysts on April 27 that it writes a $150 million layer of liability coverage in excess of $50 million for Transocean.

Mr. Charman said during the call that his company's exposure is heavily reinsured and Bermuda-based AXIS' net retention is around $8 million.

Hiscox Ltd. in London and Catlin Group Ltd. in Bermuda confirmed they are on the risk, but did not provide details of their exposure. “A lot of the loss will probably end up in the reinsurance market,” said Simon Williams, head of marine and energy at Hiscox.

Bermuda reinsurer Partner Re Ltd. said it expects $60 million to $70 million in losses, primarily within its Paris Re Holdings Ltd. unit and global specialty operations.

Montpelier Re Holdings Ltd. could see losses of as much as $20 million, the Bermuda-based reinsurer confirmed in an analysts call on April 28.

New York-based reinsurer Transatlantic Holdings Inc. said it expects insured losses to total around $1.5 billion, with its share less than 1%, or $15 million, of the industry loss.

Bermuda-based Validus Holdings Ltd. estimated its losses would range from $38 million to $45 million, net of reinstatement premiums, reinsurance and other recoveries.

Germany's Hannover Reinsurance Co. said it expects a claim of about e40 million ($53.5 million), and Munich Reinsurance Co., also of Germany, said it expects an undetermined loss related to the explosion.

—By Michael Bradford