The Federal Reserve may consider limits on bank ownership and trading of physical commodities out of concern that an event such as an oil spill could undermine financial stability.

“We are involved in a very comprehensive review” of banks' commodities activity, Fed Vice Chairman Janet Yellen said today at a Senate hearing on her nomination to become chairman of the central bank. “We want to make sure that these are conducted in a safe and sound manner, and we may be involved in additional rulemaking as we complete this review.”

Banks trade derivatives related to commodities, from oil to corn to gold. To support that business, they often accept delivery of those assets to settle trades, and even store the materials. Many banks have moved beyond trading to owning physical operations such as shipping companies and power plants.