Clifford Chance (CC) and Linklaters have scooped key mandates for Shell and BP, as the oil majors face investigation by the European Commission over allegations of oil and biofuel price fixing.

The Commission made a series of unannounced office inspections at companies, including BP, Shell, Statoil and oil pricing agency Platts on Tuesday (14 May), amid concerns the companies may have violated European antitrust rules over cartels and abuse of dominant market position.

Shell general counsel Peter Rees QC confirmed that the oil giant has instructed CC global competition head Oliver Bretz and London-based competition partner Alastair Mordaunt to advise on the matter.

Meanwhile Linklaters' competition team is understood to be advising long-term client BP in relation to the investigation. Last year the firm advised BP on its multibillion-dollar sale of Russian oil joint venture TNK-BP to Rosneft.

None of the companies were mentioned by name in the Commission's announcement but all have confirmed that they are cooperating with authorities.

The Commission's statement said the organisation had "concerns that the companies may have colluded in reporting distorted prices to a Price Reporting Agency (PRA) to manipulate the published prices for a number of oil and biofuel products". It stressed that the inspections do not mean that the companies are guilty of anti-competitive behaviour and are not a judgement on the investigation's outcome.

PRAs set benchmarks for the trade of oil in the physical and financial derivative markets in Europe and globally. Small distortions of assessed prices can have a huge impact on the price of crude oil, refined oil products and biofuels purchases and sales.

There are no legal deadlines to complete inquiries into anticompetitive conduct, but the length of the investigation is likely to hinge on the complexity, the cooperation of the companies, and the exercise of rights of defence.

Separately, Shell is currently informing firms of the result of its review of external legal advisers, with between two and five firms expected to receive appointments per practice area in each jurisdiction.