Aspen Insurance Holdings IPO gains momentum on first day.

Bermuda-based Aspen Insurance Holdings Ltd. launched an initial public offering of 10.5 million shares on Dec. 4, raising almost $240 million for general corporate purposes.

The offering by Aspen, which began trading on the New York Stock Exchange Dec. 4 under the symbol AHL, was priced at $22.50 a share for the initial 10.5 million shares, with an additional 1.6 million shares available to the underwriters to cover over-allotments, the company said. The stock rose 10.22% by mid-day to $24.80 a share before retreating somewhat to $24.10, up 7.11%, later in the afternoon.

Aspen tries to maintain maximum capital efficiency at all times, said Chief Executive Officer Chris O'Kane. As the company is ready to take on more growth--at this point more on the casualty side than on the property side--it looks at a simple solvency measure, he said.

"We're operating at about one-to-one, and we don't want to go too far from that ratio," O'Kane said. "If you want to write a couple hundred million more dollars of premium, you need a couple hundred million of additional capital. Also, with casualty rates still rising, you need the additional equity to support the rate increases."