FAS 157, a fair value accounting rule, requires banks to mark assets to their current market value, even if the market is illiquid. Some argue this is forcing banks like Citigroup and Merrill Lynch to overstate losses on investments like CDOs backed by subprime mortgages. However, others counter that marking assets to realistic current values provides transparency and that banks should have considered market risks rather than relying on theoretical values. While the intent of the rule is transparency, its effect during a crisis may be exacerbating banks' problems, according to critics like Blackstone co-founder Stephen Schwarzman.