April 4 (Bloomberg) — Brian T. Moynihan, who runs Bank of America Corp., the second-largest U.S. lender by assets, was among a group of underpaid chief executive officers last year, according to a study by pay expert Graef Crystal.

At least 99 companies in the Standard & Poor's 500 Index paid their CEOs at or below what Crystal calls their "going rate" last year, according to his study, which tracked 177 firms in the index. Moynihan, 54, was paid $13.1 million in 2013, 30 percent below what Crystal calculated as his going rate.

Chief executives typically receive boosted pay when their company's performance improves, Crystal said. When performance stalls, compensation doesn't always follow suit. Some U.S. companies have been able to tie pay to performance better than others — and improvement at those firms is happening at a "glacial pace," Crystal said.