As petrol retailers investigate reports of contaminated fuel, drivers have been contacting the BBC News website with their own experiences.
Drivers across the South East say their cars have been affected
Jonathan Earl from Barnston, Essex filled up his Vauxhall Vectra at Tesco in Harlow. He says 10 miles down the road something went wrong with the car.
"It started misfiring and juddering. I think it happened as the engine started burning the fuel I had just bought.
"I am not aware of any permanent damage as yet, but I am still trying to run the fuel down."
Wesley Williams from Milton Keynes bought his petrol on 16 February at his local Tesco. It began losing power three days later. When he took it in for repair he says the garage told him his car was not the first with these problems.
"They were surprised at the number of cars they'd had with a similar problem. The fix they're proposing is the same as the others - a new sensor.
"I'm now out of pocket by £220. My car's still in the garage while they get the part, and I have an eight-month old son who needs taking to nursery. If it is Tesco's fault I'd like them to pay for it."
Helen Perry was driving home to Standon, Herts, last week when her car lost power and began to judder. She says she had last filled up her Peugeot 307 at Morrisons in Welwyn.
"I had to pump the accelerator pedal. The engine could only get up to about 2,000 revs and no further."
She was forced to abandon her car at a garage for repairs.
"At the garage they said they'd had a few with the same problem. Even when I was collecting my car, someone else was picking up theirs. The same thing had happened."
Some garages say they're unable to cope with the excessive number of breakdowns.
Mechanic Dave Odell, who works at a garage in Northampton, says they have dealt with about 10 vehicles in the last week.
He says all the cars had broken oxygen sensors.
"A couple of dealerships have got 20-odd cars sitting there waiting for oxygen sensors. 90 per cent of them relate to one particular garage."
It was a similar story when John Butland from Peterborough took his Fiat Brava into the garage after it lost power. He says the staff there blamed petrol from Morrisons and Tesco.
"They told me I was about the tenth person they'd seen that week with the same problem."
"They drained the fuel and put in £20 worth from a different garage. It's running well now, but I'm expecting a biggish bill."