<p>Washington, May 21 (Bloomberg) -- Dynegy Inc., Duke Energy Corp. and other companies that sold power in the western U.S. in 2000 and 2001 must report their ``round-trip'' energy trades by May 31, U.S. energy regulators ordered.</p>
<p>The Federal Energy Regulatory Commission said previous transaction data was reported inconsistently and can't be used to identify such trades, which are defined as the simultaneous purchase and sale of the same amount of a commodity with the same trading partner.</p>