Biggest traders helping EU oil probe, not in it: sources

European investigators have asked top trading houses Glencore , Vitol and Gunvor to help with a probe into oil price manipulation, while not suggesting they are under investigation, industry sources said on Monday.

Last week, European Commission authorities raided the London bureau of pricing agency Platts and the offices of oil majors Statoil , Royal Dutch Shell and BP in the biggest cross-border action since the probe into rigging of Libor benchmark interest rates.

The Commission said it was concerned that companies, which it did not name, might have colluded in reporting prices to Platts to manipulate published assessments for oil, refined products and biofuels and may have prevented others from participating in the assessment process.

"We have been asked to cooperate with the investigation and provide information, so far very general. But it was also made clear to us that we are not being investigated," a source at one of the big trading houses said.

Sources at other trading houses also confirmed they had received similar requests.

Officials at the European Commission could not immediately be reached for comment.

(Reporting by Dmitry Zhdannikov; editing by Jane Baird)