BP revealed that US commodities regulators had requested information on its oil trading operations in the country.
News of the investigation by the Commodities Futures Trading Commission (CFTC) came after BP said on Wednesday that the New York Mercantile Exchange (Nymex), the world's largest oil trading house, was investigating some of its crude oil trades on a "small number of days in 2001". "The CFTC has requested information concerning BP's crude oil trading operations in the US," a BP spokesman said.
He said BP's trading activities, which span the globe on regulated exchanges and over-the-counter crude and oil product markets, continue normally on the Nymex and other exchanges.
BP said the company was fully co-operating with the CFTC and that it would be inappropriate to comment further. BP declined to disclose the timing of the trades the CFTC is investigating.
Following the collapse of US energy giant Enron and the widescale investigation of a number of power and gas traders across the country, regulators have sought to crack down on energy trading practices in the United States.
There is no suggestion that there is any parallel between the BP case and the Enron scandal.
A Houston-based oil company analyst said: "There's a heightened sense of people wanting to probe into trading these days, there's more questioning going on," he said.