So far this year, only one of 81 failed banks has ended up in the hands of private equity investors.

A group led by billionaire Wilbur Ross and including buyout giants Blackstone Group and Carlyle Group picked up BankUnited in Florida. Since then, there have been none, though banks are failing at a rate of about five a week.

That could change under a set of rules adopted by the FDIC board Wednesday, which establish the level of capital that private equity firms have to inject into the banks that they buy. Though tougher than existing rules, the FDIC’s new stance is not as tough as proposals FDIC boss Sheila Bair made in July. The compromise rule could open the door to more private equity activity in the banking business. Ross said that door won’t open as wide as it would have if the FDIC had not required higher capital requirements for private equity firms than it requires for banks buying failed banks.

“They modified it enough that we can get back in the game, but not as effectively as I would like,” said Ross.

Bair proposed in July that when private equity firms buy banks, they would have to maintain a ratio of capital to assets at 15 percent. A bank is considered well capitalized when it keeps that ratio, called a Tier 1 leverage ratio, above 5 percent. The 15 percent proposed requirement brought protests from private equity players.

The FDIC reached for middle ground today, reducing the capital asset ratio for private equity firms with no experience running banks to 10 percent. The FDIC board also dropped plans to make private equity investors a “source of strength” for banks, potentially leaving them on the hook for bank losses. The board encouraged private equity firms to partner up with bank holding companies so that they could avoid the higher capital requirements.

Ross said the 10 percent level would drive down the bids he and other investors might be willing to make for failed banks—causing them to lose out on those deals. He had proposed a 7.5 percent requirement, which he said was higher than the bank standard but low enough to entice private equity players to bid more aggressively for failed banks held by the FDIC. “I think people will bid, we just will not be able to bid as high a price as if they had accepted my recommendation of 7.5 percent," he said.

And that could cost the FDIC billions of dollars, he said. “Even the 10 percent is costing them some value and consequently they would be better off with a lower number," Ross said. He urged the FDIC to ease the 10 percent requirement when it reviews the rules in six months.