OSLO (Reuters) - The European Commission said on Tuesday it was investigating major oil companies over suspected anti-competitive agreements related to submission of prices to reporting agency Platts.

Royal Dutch Shell , Norway's Statoil and Platts all said they were cooperating fully with the investigation.

Platts is the world's biggest oil price reporting agency, and its physical market assessments form the basis of billions of dollars worth of oil sales around the world.

Statoil said authorities had inspected its office on the request of the European Commission on suspicions of anti-competitive behavior.

"The authorities suspect participation by several companies, including Statoil in anti-competitive agreements and/or concerted practices contrary to Article 53 of the EEA Agreement," the company said.

"In addition the inspection relates to potential abuse of possible dominant position by another party, contrary to Article 54 of the EEA Agreement," it added.

Statoil also said in a statement the suspected violations are related to the Platt's market-on-close (MOC) price assessment process, used to report prices in particular for crude oil, refined oil products, and may have been ongoing since 2002.

The company said it was cooperating with the authorities.

Platts said the European Commission had "undertaken a review at its premises in London this morning in relation to the Platts price assessment process."

It said it was fully cooperating with the review.

It was not clear whether other companies are included in the investigation.

Shell also confirmed that its affiliates are assisting the European Commission in an enquiry into trading activities.

Thomson Reuters , parent of Reuters news, competes with Platts in providing news and information to the oil market.

(Reporting by Nerijus Adomaitis; editing by James Jukwey and Jane Baird)

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