Petrol station managers urged motorists across Oxfordshire not to panic buy tonight, as 500 tanker drivers prepared for a four-day walkout.

Members of the Unite union employed by two firms working on Shell contracts are due to walk out at 6am on Friday in a pay dispute which could hit one in ten filling stations across the country, including 11 in Oxfordshire.

Harry Kumar, manager of Shell's filling station at the Pear Tree roundabout, Oxford, said people were buying more fuel than usual.

He said: "People were panicking. Normally we are busy up to 10am and then again at lunchtime, but it was really busy all morning.

"One lady said she was filling up to last two weeks so she didn't have to worry. People were asking questions about what was going to happen."

But Mr Kumar added: "I don't think we are going to have a big problem unless people panic buy."

Other petrol stations in the county also warned against panic buying over the weekend, although few said they had noticed a significant increase in sales yet.

Don Ezason, manager of the Barrington Filling Station, Burford, said this afternoon: "We have been a bit busier, but nothing special - we haven't got them queuing out of the forecourt like a few years ago.

"There is plenty of petrol about and if people are sensible there will be enough for everybody."

Tony Hallan, who manages Shell petrol stations in London Road, Headington, and Park Street, Thame, said: "It was busy first thing in the morning, but it's normally busy first thing in the morning.

"If our tanks are full or three-quarters full on Thursday evening we will have enough fuel on site to see us through.

"If people start to panic buy we will have a problem, but Shell is a huge company and I have no doubt it will have been through this situation before."

The pay row erupted because Unite members claim they are paid the same now as in 1992 - just under £32,000 a year - despite working longer hours.

Bernie Holloway, spokesman for Hoyer, the biggest of the two transport companies involved in the dispute, said it was "disappointing" Unite had rejected an improved pay offer last week.

Unite repeated calls for Shell to get involved. Assistant general secretary Len McCluskey said: "It's no use Shell bosses sitting on their hands."

The petrol giant has so far refused to get involved in the dispute.