Five major freight rail companies overcharged customers more than US$6.5 billion under the guise of fuel surcharges, according to a study commissioned by businesses that are accusing US railroads of anti-competitive behaviour.

"This is the greatest train robbery of the 21st century," said Jack Gerard, president and chief executive of the American Chemistry Council, which represents about 90 percent of the nation's chemical makers.

The council commissioned an economic analysis that found the railroads' fuel surcharges were excessive by more than $6.5 billion between 2005 and the first quarter of 2007. The study was based on regulatory filings and other estimates for Union Pacific Corp, Burlington Northern Santa Fe Corp, Norfolk Southern Corp, Kansas City Southern and CSX Corp.

Federal regulators in January banned excessive fuel surcharges and imposed strict rules on the fees that many rail companies have openly credited with bolstering their earnings.

The Surface Transportation Board ruling said the railroads must link the surcharges directly with the actual fuel costs for specific rail shipments and prohibited "double-dipping," which means fuel costs can't be calculated into certain price hikes if the shipments already have other fuel surcharges.

But the board has no authority to enforce refunds or seek penalties, Gerard said, adding that railroad customers currently lack any regulatory means to attempt to recoup the money. Still, some have filed lawsuits alleging the fuel surcharges amounted