The EU Commission has searched the offices of several companies in the gas sector in Germany.
The authority is investigating the suspicion that the companies have violated competition rules and may have abused their market power, they said on Thursday.
The searches had already taken place on Tuesday.
The focus is on companies that are active in the supply, transport or storage of natural gas.
The authorities did not name names.
Reuters reported on Wednesday that the commission had searched the offices of Russian gas giant Gazprom in Germany.
However, this has still not been officially confirmed.