The boss of Italian energy company Eni, Paolo Scaroni, is under investigation as part of a police probe into alleged gas pricing irregularities.
Eni boss Paolo Scaroni said he is 'serene' about the investigation
The chairman of Milan-based utility AEM, Giuliano Zuccoli, is also being investigated by police.
Italy's financial police, the Guardia di Finanza, are looking into whether meters used for measuring the amount of gas sold to companies were misused.
Mr Scaroni said that he was "serene" about the probe.
A statement from Eni stressed that household bills were not involved.
The probe is centring on non-booked gas, which is the difference between the price of gas that Eni buys from its suppliers and the price of gas that the company then sells on to its distributors.
Financial police have taken documents from the offices of Eni's gas distributor Snam Rete Gas and its gas retail unit Italgas.
The chief executive of Snam Rete Gas, Carlo Malacarne, and the chairman of Italgas, Giovanni Locanto, are also being investigated.