Bumper-to-bumper queues are a common sight

Negotiations between Transport Minister Jean-Claude Gayssot and the unions have so far failed to bring an end to the dispute.

There are also signs that the protests are set to spread to other European countries, with farmers and truck drivers in Spain and Belgium threatening similar action later this month.

Panic buying

The protesters, who have formed barriers outside 60 out of 70 of the country's oil depots, are demanding cuts in fuel taxes of about 20%.

Police say that in the eastern town of Dijon, 80% of petrol stations are out of fuel, and around the southern city of Marseille, nearly half of the petrol stations have been pumped dry.

Across the country, authorities are beginning to take measures to control panic-buying.

In Lyon, petrol stations have been told to turn motorists away and supply only doctors, hospitals and emergency services.

In the southern Var and Rhone departments, petrol stations have been ordered to sell only a maximum of FF150 ($20) of diesel to light vehicles, or FF200 of petrol.

Some motorists have been crossing from south-western France into Spain to fill their tanks.

The situation appears set to worsen, with taxi drivers, owners of private ambulances and bus companies pledging to join the action.

Protesters lit fires on the edge of a railtrack on Tuesday morning, stopping the high-speed Bordeaux-Lille TGV.

Minister hopeful

In Paris, Mr Gayssot went into a third round of talks with representatives of the haulage industry, expressing optimism that a breakthrough to end the crisis might be imminent.

He said: "I think that the situation will be resolved during the day.

"There is some way to go, but I think there is a will to reach a conclusion."

In talks on Monday night, the government offered a reduction in fuel tax of about half the 50 centimes per litre (six US cents) demanded by the unions.

One union negotiator, Daniel Chevalkier of the UNOSTRA federation said: "The government proposals are for the moment totally insufficient."

Most fuel depots have been blockaded

Last week French fishermen won big concessions after blockading ports, and the BBC Paris correspondent says the government has hinted that it is prepared to do something similar this time.

The unions want a reduction in fuel taxes in order to bring down the price of fuel which has risen 50% in the past 18 months, following a steep rise in world oil prices.

The blockade, by up to 2,000 vehicles, has hit important plants, including depots at Fos-sur-Mer near Marseille, at Donges on the Atlantic coast near La Rochelle, at Le Havre and Dunkirk on the northern coast and at Grandpuits east of Paris.

Mr Gayssot has called for concerted EU pressure on oil producing countries (Opec) to lower oil prices.

He said: "It seems to me that Europe, including the European Central Bank, should express its determination to hold talks with the Opec countries and tell them 'you cannot do just anything'."