American Electric Power ( AEP) said it has received an informal inquiry from federal regulators regarding so-called round-trip energy trades, which are the simultaneous exchange of contracts that can artificially inflate trading volume.

The request from the Securities and Exchange Commission is the latest in a series of government inquiries into the trading practices of energy companies, a list that includes Dynegy ( DYN), Reliant Resources ( RRI), CMS Energy ( CMS), Duke Energy ( DUK) and El Paso ( EP).

AEP, based in Columbus, Ohio, said it plans to cooperate fully with the SEC's request.

AEP previously disclosed that after completing a review of its trading activities from Jan. 1, 1999, through March 31, 2002, the company identified transactions that involved sequential trades with the same terms and counterparties, which amounted to one-quarter of 1% of total trading volume.

"The total contribution of these transactions to gross revenue is not material," AEP said in a press release. "The company believes that substantially all of these transactions involve economic substance and risk transference and do not constitute 'round trip' or 'wash' sales."

Shares of AEP were recently down 61 cents, or 1.8%, to $34.32 on the New York Stock Exchange .