Industrial action over the past three weeks has seen every French refinery debilitated to some extent, hindering fuel deliveries throughout the country and hurting European crude prices as market players look to sell.

The action is part of a nationwide movement against pension system changes championed by President Emmanuel Macron, including raising the retirement age by two years to 64.

The shut-in of French refineries has weakened crude oil markets in Europe. The absence of French demand has increased supplies of crude grades from the North Sea, west Africa and blends from the Caspian pipeline, according to traders.

"It's a pretty bad situation," one of the traders said.

Meanwhile, the strike action is tightening supply of refined oil products such as diesel and gasoline. In a sign of these concerns, the spread between the prompt and second month ICE low-sulphur diesel contracts remained high at around $21 per tonne, known as a backwardation.

Meanwhile, gasoline refining margins rose on Friday to their highest since October at around $23/bbl.

About 17% of all fuel stations throughout the country were missing at least one product as of Monday night, France's petroleum association UFIP said, citing French energy ministry data.

The rate of missing stocks is always higher coming out of the weekend and is set to improve from Tuesday, UFIP added.

About 29% of fuel stations in the Ile-de-France region, where capital city Paris is located, were missing at least one product, the data showed.

Two regions in the south of France were missing 28% and 24% respectively, the Brittany region was missing 29% and an eastern region was also missing 29%, the data showed.

The strikes have also caused disruptions at airlines, where France's civil aviation authority DGAC asked companies to cut flights by 20% from Paris-Orly on March 30 and by 25% on March 31.

Airlines have previously had issues receiving jet fuel kerosene as the depots that deliver it have been blocked.

"We did see a big negative impact (with jet fuel) last week, but this week it's going to turn as Le Havre is opening up," according to a separate trader.

This comes as the refining sector enters its 21st day of industrial action, which has stopped production at France's two biggest refineries and forced three others to operate at reduced capacity. The other two French refineries have been offline for repairs.

The Petroineos Lavera refinery in the south of France has had rolling closures for about a week, with several units shuttered on alternating days and with the main unit closed, Sud Chimie union representative Gaetan Basset said.

"The only thing that could change at (Lavera) is a resumption of work and an exit from the movement, but as of today we're far from finished," Basset said.