(Adds details on Enbridge system, quote)
By Nia Williams
CALGARY, Alberta, Feb 4 (Reuters) - A U.S. investigationinto oil major BP Plc breaking anti-fraud and reportingrules on using oil pipelines is related to crude shipped onEnbridge Inc's Mainline system, Enbridge said onWednesday.
Graham White, a spokesman for Canada's largest pipelinecompany, confirmed the investigation is related to crude volumesnominated by shippers on its system. He said the CommodityFutures Trading Commission (CFTC) had not indicated Enbridge wasunder investigation.
"We are prevented from publicly commenting on this matter ascompany information will be required for the investigations,"White said. "Our downstream nominations process was reviewed byFERC in 2013 and approved as 'just and reasonable'."
The CFTC told BP last November it planned to recommend anenforcement action alleging violations of the Commodity ExchangeAct in connection with Canadian pipeline nomination proceduresand related trades, BP said in a quarterly earnings statementTuesday.
The British oil giant said it submitted a detailed defenceto U.S. regulators in mid-December.
"We have responded to the CFTC's allegations and challengedtheir jurisdiction over the alleged conduct," said a companyspokesman.
Sarah Kiley, spokeswoman for Canada's National Energy Board,the country's energy and safety regulator, said at this pointthe NEB was not involved in the investigation.
Enbridge's 2.2 million barrel-per-day Mainline system shipsthe bulk of Canadian crude exports to the United States.
It also supplies BP's 413,500 barrel-per-day Whiting,Indiana, refinery, which in 2013 underwent a major revamp so itcould run more heavy Canadian crude.
Limited export capacity between Canada's growing oil sandsand U.S. refining markets mean export pipelines are routinelyoverbooked, with shippers nominating more crude than there isspace for.
In 2013, Enbridge altered how it calculates the amount ofcrude shippers can nominate to help eliminate "air barrels" -referring to nominations that are higher than the physicalvolume shippers can move.
Under the new system, approved by the Federal EnergyRegulatory Commission (FERC), shippers calculate how much crudethey can request to ship based on the capacity of downstreamrefineries. Enbridge then verifies the nominations itself.
The changes met with fierce resistance from many traders inCalgary, who argued the new system favoured the biggestrefineries and gave Enbridge too much discretion. (Additional reporting by Nia Williams; Editing by Bernard Orrand Jessica Resnick-Ault)