An investigation has begun into claims oil prices may have been fixed for over a decade which could have resulted in petrol prices and energy bills being kept artificially high.

The London headquarters of BP and Shell have been raided by European Union watchdogs over allegations they colluded to rig prices.

The Commission said it had launched the investigation over suspected anti-competitive agreements related to the submission of prices to Platts, the world's leading oil pricing agency.

"Officials carried out unannounced inspections at the premises of several companies active in and providing services to the crude oil, refined oil products and biofuels sectors," the EU's executive arm said in a statement.

"The commission has concerns that the companies may have colluded in reporting distorted prices to a price reporting agency to manipulate the published prices for a number of oil and biofuel products. Furthermore, the commission has concerns that the companies may have prevented others from participating in the price assessment process, with a view to distorting published prices," it added.

"Cooperating fully" with investigation 

The statement did not identify the companies involved, saying the inspections had taken place in two EU member states and one non-EU country. The 3 companies confirmed they are subject to the inquiry.

A Royal Dutch Shell spokesperson said "We can confirm that Shell companies are currently assisting the European Commission in an enquiry into trading activities. We are fully cooperating with the investigation," the spokesperson said, declining to comment further for legal reasons.

A BP statement also said the company was "cooperating fully" with the probe.

Statoil said the inspection, at its headquarters in Stavanger, Norway, had been carried out with the assistance of Norwegian antitrust officials. Norway is not part of the EU. It said the suspected violations may have been on-going since 2002.

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

"Platts is cooperating fully with the European Commission's review."

The investigation - one of the biggest cross-border actions since the Libor rigging scandal - had no impact on the London-listed share prices of BP or Shell on Tuesday though Shell's value dipped by more than 1% early on Wednesday.

The Commission said even small distortions of assessed prices may have a huge impact on the prices of crude oil, refined oil products and biofuels purchases and sales, potentially harming final consumers. It said EU officials were accompanied by their counterparts from the national competition authorities, and stressed that the fact such inspections had been carried out did not mean the companies were guilty of anti-competitive behaviour.