A strike squeezing French oil refineries spread Tuesday to facilities owned by ExxonMobil Corp., raising the pressure on Total SA and the government to ward off gas shortages.

Workers at an ExxonMobil-owned Esso depot joined in the walkout Tuesday to support their Total colleagues, who have been striking since last week over plans to close a plant in northern France.

The Esso depot in Port Jerome, on the English Channel, was closed before dawn for lack of workers, CGT union organizer Laurent Delaunay said. Workers at an Esso refinery in neighboring Notre-Dame-de-Gravenchon _ France's second-largest refinery _ were set to walk out later Tuesday.

Together, Total and Esso refineries account for about 70 percent of France's refining capacity.

A prolonged strike and serious gas shortages could be bruising for French President Nicolas Sarkozy's government as it faces regional elections in less than three weeks. The refinery blockages come amid other acts of unrest among French workers, including an air traffic controllers' strike canceling hundreds of flights Tuesday.

Sarkozy summoned Total CEO Christophe de Margerie for talks on the refinery strike Tuesday.

Total, France's largest company by market capitalization, is meeting with unions for new negotiations Tuesday at the company's headquarters in La Defense, a business district west of Paris.

The first signs of shortages were beginning to appear. On Tuesday, a Carrefour service station in Gonfreville, home to France's largest oil refinery, was out of diesel fuel.

Total said more than 100 of the 2,000 Total and Elf gas stations in France had run out of at least one type of gasoline.

Environment Minister Jean-Louis Borloo insisted that "at this point, there is no risk" of widespread shortage. Speaking on Europe-1 radio, he said France has about 10 days worth of reserves, and called for calm.

Workers at all six of Total SA's French refineries and at six of its 31 fuel depots have been on strike for five days over the uncertain future of a plant in Dunkirk.

Total says it is preparing new uses for the Dunkirk site and that its activities have been stopped since September because of a drop in consumption of petroleum products manufactured there. The CGT union, which represents a majority of workers in the conflict, insists that Total's Dunkirk refinery must continue to run as it has in the past.

Total's refineries are losing euro100 million ($135 million) a month, spokesman Michael Crochet-Vourey said.

Workers at France's fourth-largest refinery, British-owned chemicals company INEOS, also voted Monday to join the strike. Two more refineries, owned by Switzerland's Petroplus, are scheduled to take a strike vote on Wednesday.

Total shares have so far been little affected by the strikes, however. Shares were down about 0.5 percent to euro42.46 in midday Paris trading.