The European Commission launched an investigation involving BP, Royal Dutch Shell and Statoil for alleged price manipulating through Platts, a division of McGraw Hill.
A spokesman for British Prime Minister David Cameron said the companies involved were expected to comply fully with the investigation.
"It would be deeply worrying if prices had been driven up for households, especially given all the work government had been undertaking to deal with the cost of living," he said in a statement. "The European Commission investigation should run its course as it was critical it got to the bottom of the issue."
European investigators alleged that companies provide false oil information to Platts, which publishes prices used to set costs that refiners pay for crude oil.
Statoil, which had its offices raided this week, said the suspected violations may date to 2002. The London offices of Platts were inspected Tuesday.
"Any such behavior, if established, may amount to violations of European antitrust rules that prohibit cartels and restrictive business practices and abuses of a dominant market position," British Energy and Climate Change Secretary Ed Davey said in a statement.