The addition of Sideris Re will increase Torus' capital by about $79 million, Torus said in a statement.

Syndicate 2243 writes a worldwide portfolio of upstream and offshore energy risks as well as non-U.S. and Canadian onshore business. This business is written under an agreement with Starr Managing Agents Limited, Torus said. SMA is a subsidiary of C.V. Starr & Co. Inc.

A.M. Best Co. in Oldwick, N.J., said today that its ratings of Torus Insurance Holdings Limited (Torus) (Bermuda) and its operating subsidiaries remain unchanged following the contribution of Sideris Re Holdings Ltd to Torus by First Reserve Corporation (the sole shareholder of Torus).

Best said SRH owns 100 percent of First Reserve Corporate Member Limited (to be renamed Torus Corporate Capital Limited), which provides 100 percent of the underwriting capacity of Lloyd's Syndicate 2243.

Although this transaction "represents a departure from the group's original plans for 2009-2010," Best said it believes the consolidated risk-adjusted capitalization of Torus will remain strong.

The rating agency said the transaction is sufficient to support Syndicate 2243's agreed capacity for 2010 of ?43 million ($70.1 million). Syndicate 2243 writes a joint book of energy business with Lloyd's Syndicate 1919, with a 22 percent share of Syndicate 1919's international onshore energy business and a 38.875 percent quota share of Syndicate 1919's worldwide offshore energy book.

Both Syndicate 2243 and Syndicate 1919 are managed by Starr Managing Agents Limited., A.M. Best said.

Commenting on the merger Mark McComiskey, managing director, First Reserve Corporation, said, "The amalgamation of our insurance operations, under the management of Torus, is a logical step for all parties."

Clive Tobin, Torus' chief executive, said the "Sideris business complements our own existing energy portfolio, increasing our underwriting flexibility and underlining a growing commitment to serving clients in this sector."