Watchdog probes fuel price-fixing
However, some analysts are dismissing the move, claiming it is a pre-election stunt by the government, designed to punish big business.
Energy Department Chief Aleksandr Pirozhenko says higher export rates and reduced demand should have brought prices down.
But some commentators are sceptical of the timing. Punishing fat-cat oil giants ahead of December's Duma election could be seen as a perfectly-timed populist move by the government.
However, Petromarket CEO Yakov Ruderman says officials are failing to understand what's behind the price rises
‘The government would do better to set the bi-monthly export tariffs weekly or even daily, because that’s what causes the price hikes,’ Mr Ruderman said.
Oil firms blame the production slump on essential plant repairs and an accident at the vast Ryazan refinery.
But it's unclear whether the FAS will accept the explanation. The monopoly watchdog has already fined cartels in Russia's biggest sectors, including dairy and mobile operators
So, the likes of Rosneft and Lukoil won’t be happy to find the regulator on their tail.