A group of oil companies are being investigated by the European Commission over allegations of price-fixing.
The Commission said a series of unannounced inspections were carried out by its officials on oil companies, including BP, Shell and Statoil, yesterday.
It said that unannounced inspections are a preliminary step to investigating suspected anti-competitive practices and do not mean that the companies are guilty of any wrongdoing. There is no legal deadline to complete inquiries.
A spokesman for BP said: "BP is one of the companies that is subject to an investigation that was announced earlier today by the European Commission. We are co-operating fully with the investigation and unable to comment further at this time."
Norwegian company Statoil confirmed its office in Stavanger was inspected today and Shell said it was being investigated, with its offices in London and Rotterdam being visited.
A Shell spokesman said: "We can confirm that Shell companies are currently assisting the European Commission in an inquiry into trading activities. We are fully co-operating with the investigation. For legal reasons we cannot make any further comment at this stage."
A statement from the Commission said: "The European Commission can confirm that, on 14 May 2013, commission 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 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.
"Any such behaviour, if established, may amount to violations of European antitrust rules that prohibit cartels and restrictive business practices and abuses of a dominant market position (Articles 101 and 102 of the Treaty on the Functioning of the EU and Articles 53 and 54 of the EEA Agreement)."
The European Commission statement added that even small distortions of assessed prices could have a "huge impact on the prices of crude oil, refined oil products and biofuels purchases and sales, potentially harming final consumers".
RAC technical director David Bizley says the allegations were "worrying news for motorists" who are already suffering due to the high cost of keeping a vehicle.
"The Office of Fair Trading inquiry concluded at the end of January that the UK fuel market was operating fairly and not against the best interests of motorists, and therefore that a Competition Commission investigation was not needed,” he said.
"Motorists will be very interested to see what comes of these raids. Whatever happens the RAC will continue to campaign for greater transparency in the UK fuel market and for a further reduction in fuel duty to stimulate economic growth. "
Tory MP Robert Halfon has led a campaign calling for a full investigation into alleged cartels and market manipulation in the oil market for the past three years.
The Harlow MP, who founded the www.PetrolPromise.com website to campaign for cheaper petrol and diesel, said: "Last year, in a debate that I pressed for, Parliament voted unanimously for an investigation into the oil market.
“These latest allegations underline why that must happen urgently in the UK. High oil prices are crushing families across Britain. Motorists are being taken for a very expensive ride.
"The government has done its bit, by freezing fuel duty for three years. Now oil companies must come clean and show some responsibility for what is happening to the international oil price."
Shadow energy and climate change secretary Caroline Flint said: "These are very concerning reports, which, if true, suggest shocking behaviour in the oil market that should be dealt with strongly.
"When the allegations of price fixing in the gas market were made, Labour warned that opaque over-the-counter deals and relying on price reporting agencies left the market vulnerable to abuse.
"These latest allegations of price fixing in the oil market raise very similar questions. Consumers need to know that the prices they pay for their energy or petrol are fair, transparent and not being manipulated by traders."