Bermuda-based reinsurer Aspen Re plans a US initial public offering that would value it at more than $1 billion and has named Credit Suisse First Boston and Goldman Sachs as lead banks, said sources familiar with the company.

Aspen Re, which was spun off from Lloyd's insurer Wellington Underwriting Plc in May 2002, specialises in property and casualty reinsurance in the UK, United States and Bermuda.

Reuters said the reinsurer, whose holding company is based in Bermuda, has long been mooted as an IPO candidate. One source familiar with the company said its listing plans had been kept on ice due to poor market conditions.

An IPO is not imminent, with a US listing likely at the start of next year, the source said.

A spokeswoman for the company declined to comment. Goldman Sachs and CSFB, which owns 12 percent of Aspen through CSFB Private Capital, also declined to comment.

The reinsurer will be valued at around 1.2 to 1.4 times book value, in line with many of its US peers, said another source familiar with the company. Aspen Re's net asset value was 575 million pounds on June 30, which would give it a valuation of 700 million to 800 million pounds, or $1.2-$1.3 billion.

"It would make more sense to be listed in the US, despite being UK based, given that it shares more similarities with its US quoted peer group," said Nick Johnson, an insurance analyst at Numis Securities.

Aspen recently expanded into the US by buying Dakota Speciality Insurance Company from The Insurance Corporation of New York.

Other investors include U.S private equity firm The Blackstone Group, which owns almost a third of the company, Wellington Underwriting Plc, Candover Partners Limited, Bermuda-based Montpelier Reinsurance and 3I Group Plc.

Johnson at Numis Securities said there would be reasonably healthy demand for an Aspen IPO, given the strong trading environment for the insurance sector.

However, the window of opportunity is finite. Insurance premiums, which have risen since the terrorist attacks of September 11, are now showing signs of peaking, he added.

Aspen Insurance Holdings Ltd. was established in June 2002, and has operating subsidiaries, Aspen Insurance UK Ltd. and Aspen Insurance Ltd.

Aspen Insurance UK Ltd. is rated A by Standard & Poor's Corp and A2 by Moody's Investor Corp.

In a recent report, S&P said Aspen has a strong business position, operating performance and capital adequacy, and a proven management team.

However, "these factors are offset by the potential operational volatility and cyclicality inherent in the class of business that it conducts and its high reliance on reinsurance", the report added.

According to Aspen's website, in the third quarter of 2002 the overall group had revenues of $67.6 million and a net income of $15.5 million.