Police fired water cannon to disperse activists blocking an oil depot in the northeast, but six out of eight of France's refineries were still either at a standstill or had sharply reduced their output.
The head of the oil industry federation (Ufip) said that with a fifth of petrol pumps running dry, it had begun using strategic reserves.
"For the past two days, since there have been operational problems at the refineries and blockades of depots, we have... been using reserve supplies," Francis Duseux told French radio.
The CGT union, locked in an increasingly bitter struggle with the government, has threatened to extend its action to nuclear power stations tomorrow.
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It has urged "the biggest action possible" on a day when unions have called for a broad day of strikes and demonstrations across the country.
One nuclear power plant in Nogent-sur-Seine, around 100 kilometres southeast of Paris, is already operating at reduced capacity.
One of the two reactors has been out of operation since Tuesday "due to a technical problem" and "we will ensure that it is not re-started", said Arnaud Pacot, the local CGT representative.
Riot police used force to break a blockade at an oil depot in Douchy-les-Mines near the Belgian border that had been in place since Thursday.
Watched by around 80 striking workers, firefighters extinguished burning tyres that were blocking roads, sending thick plumes of smoke billowing into the air.