Brussels - Gas companies in 10 countries were raided on Tuesday by EU inspectors, amid suspicion that they may have violated competition laws, according to the bloc's executive.
Germany's biggest gas provider Eon Ruhrgas, the German subsidiary of Russia's Gazprom and Austria-based OMV confirmed that they are subjects of the probe.
The European Commission did not name the companies, but said the firms under investigation supply, transmit and store natural gas.
"The commission is investigating potential anti-competitive practices in the supply of natural gas in Central and Eastern European member states," it said in a statement, noting that the inquiry is focused "on the upstream supply level".
The commission said it suspects the companies divvied up markets among themselves, blocked competitors from accessing pipelines and possibly drove up prices.
"Gazprom has nothing to hide and calmly awaits the investigations," said Burkhard Woelki, spokesperson of Gazprom Germania.
Gazprom's Czech subsidiary was also raided, the German business weekly Wirtschaftswoche reported online.
OMV spokesperson Sven Pusswald said: "I can confirm that we are cooperating with the commission," a position echoed by Eon and Gazprom.
OMV is active in several Central and Eastern European countries.
None of the three companies commented on the substance of the allegations.
The commission said it is dedicated to ensuring "the diversification of sources of supply and the free flow of gas once it has entered the EU".