It is understood that the commodities trading firm – which recently merged with miner Xstrata – is one of many companies that have now been contacted by the EU antitrust regulator.
Fellow Swiss-based commodities trading houses Vitol, Gunvor and Mercuria have also reportedly been asked to submit information.
However, there is no suggestion that they are under investigation.
Allegations of price-fixing rocked the oil industry last week, when BP, Shell, Statoil, ENI and price reporting agency Platts all confirmed that they were being probed by the EC.
The EC said that it had carried out unannounced raids on the premises of several companies on the suspicion that they were manipulating oil prices.
The EC said it was concerned that companies might have colluded in reporting prices to Platts to manipulate published assessments for oil, refined products and biofuels.
The investigation has already drawn comparisons with the Libor scandal, which has seen several banks receive fines for manipulating interbank lending rates.