Published: May 07, 2010 10:39 PM EDT

WASHINGTON (AP) - The federal regulators that oversee financial markets say they are investigating the causes of the mass sell-off Thursday that pushed the Dow Jones Industrial average down hundreds of points.

They are identifying one possible cause: Conflicting trading rules for different markets. The Securities and Exchange Commission and the Commodity Futures Trading Commission say they are reviewing data related to Thursday's trading frenzy.

They are looking at information from exchanges, self-regulatory groups and market participants. They say they will make any necessary changes to prevent the problem from recurring.

The SEC and CFTC have ultimate oversight of financial markets, but they generally rely on the markets to write and enforce their own rules.