NEW YORK (Bloomberg) — Ace, XL Capital, American International Group and Chubb Corp. may face higher claims from insuring corporate customers against litigation expenses as more investors file lawsuits amid falling stock markets, Standard & Poor's said.

"Historically, as stock-market performance worsened, the number of investor lawsuits has tended to increase," analysts led by Damien Magarelli wrote in a note to investors. The legal costs could lead to higher claims for the insurers in "the next few years," the report said.

Sales of coverage protecting directors and officers against legal expenses have surged as investors sued 166 US companies claiming stock fraud in 2007, 43 percent more than in 2006, according to a January study released by the Stanford Law School Securities Class Action Clearinghouse and Cornerstone Research. The S&P 500 dropped 3.8 percent in the last three months of 2007 and has slipped in every quarter since.

AIG, Chubb, Ace, Hartford Financial Services Group and Bermuda-based XL are among the leaders in sales of D&O coverage, S&P said in a report today.

"There is a precedent for D&O exposures to contribute to both substantial losses and negative rating actions," Magarelli wrote.