NEW YORK (Bloomberg) — Bermuda-based Primus Guaranty Ltd., a manager of $21.3 billion in credit-default swaps, said second-quarter earnings more than doubled as credit markets rebounded and it bought back debt at a discount.

Net income jumped to $596.9 million, or $14.46 a share, from $262.6 million, or $5.78, a year earlier, the company said yesterday in a statement. Excluding changes in the market value of the contracts, on which Primus doesn't post collateral to its bank clients, the company said it earned $1.15 a share, up from 41 cents a year earlier.

Primus, led by chief executive officer Thomas Jasper, is seeking to rebuild itself after its unit that sells credit-swaps guarantees was shut out of the market last year. The company is restructuring its existing credit-swaps trades, repurchasing debt at a discount and expanding or developing other businesses.

Revenue surged to $609 million last quarter from $278.3 million a year earlier, the company said.

Primus's credit-swaps unit, once given the highest ratings by Standard & Poor's and Moody's Investors Service, this year was cut to a level that prohibits it from selling new contracts after having to pay out almost $146 million, or 18 percent of its capital, following the bankruptcies of Lehman Brothers Holdings Inc. and Washington Mutual Inc., and the Icelandic government's seizure of its three largest banks.