S&P analyst and report author Robert Green said that public ownership does not lend itself to the capitalization of start-up or newer bond insurers, “and it certainly didn't lend itself to capitalization when this industry and the financial guaranty concept were new.”

“Theoretically, a combination of both public and highly rated strategic ownership, where the strategic owner has a material investment, may be the best possible ownership profile,” Mr. Green wrote.

The next most desirable ownership structure was 100 percent strategic ownership. “Ideally, strategic owners are highly rated and view the financial guaranty unit as bringing benefits to the consolidated operations beyond earnings,” he wrote.

But having only one strategic owner could pose a challenge if that owner should suffer a ratings downgrade, such as the case with XL Capital.

Both majority and 100 percent public ownerships have their downside in that market conditions or adverse development at the bond insurer may make it difficult for management to sell shares at an unattractive price.

“Another challenge associated with the public equity market is the strong emphasis placed on quarterly results by market participants,” Mr. Green said.