The map above is a snapshot of where people who have contacted BBC News say they have bought petrol that has led to engine problems
By 1730 GMT the website had received more than 4,600 e-mails and texts from motorists complaining of problems with their cars after buying fuel
Initial reports centred on petrol bought at Tesco and Morrisons forecourts in south-east England, although both companies have said no fault has been found with their fuel
And the map shows clearly that motorists are reporting that petrol stations all over the country have been hit
http://news.bbc.co.uk/1/hi/uk/6409025.stm
Where you've been buying 'faulty' fuel
Fuel depot probes 'contamination'
Thousands think they have been affected by the problems
A depot allegedly linked with the "contaminated" fuel said to have damaged car engines is investigating whether it is to blame for the problem.
Meanwhile, an AA source told the BBC traces of silicon have been found in petrol taken from the cars.
Thousands of drivers have complained their cars were damaged after they used petrol from supermarket forecourts.
Tesco said the problems appeared to be linked to forecourts in the south east of England served by a site in Essex.
Both Tesco and Morrisons get fuel from an independent oil company called Greenergy, which insists its supplies meet industry standards.
I've been in this industry for over 30 years and I don't remember anything like this happening before
Ray Holloway,
Petrol Retailers Association
Mr Holloway interview
A major Greenergy storage depot is run by distribution firm Vopak on the River Thames at West Thurrock, Grays, Essex.
Colin Scott, Vopak Terminals managing director, said checks were being made to make sure normal handling and storage procedures have been followed.
"Verifications are continuing. At this moment we have not established any deviation from normal procedures."
The AA source said tests carried out by the petroleum industry had revealed traces of silicon in suspect fuel. The substance should not be in unleaded petrol.
'Faulty' fuel locations
It is thought silicon may have found its way into a batch of petrol in transit by ship into the UK or in storage containers.
Trading standards officials said their tests on the suspect fuel may be available on Friday.
The Trading Standards Institute said samples of unleaded petrol had been taken from station forecourts in Cambridgeshire, Kent, south Essex and Milton Keynes.
A spokeswoman said spot checks were also being undertaken by local authority trading standards teams in other parts of the country.
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Petrol questions answered
Tests on fuel supplied by Tesco, Morrisons and Asda have so far not revealed any problems, the supermarkets have said.
The penalty for supplying fuel which does not meet industry standards is a £5,000 fine.
The BBC has received more than 3,500 e-mails from motorists who say their vehicles have juddered, misfired and suffered a loss of power.
Most came from an area covering London and parts of east and south-east England and many reported buying petrol from forecourts at supermarkets.
But problems have also been reported by motorists in other areas including Aberdeen, Manchester, Newcastle and Preston.
The Association of British Insurers (ABI) said motorists affected by contaminated petrol should be able to claim if they have comprehensive cover.
Repair bills
The problems seem to be centred on oxygen sensors in vehicles.
The sensors are attached to the exhaust and determine the mix of oxygen and petrol supplied to the engine.
Garages are running out of replacement parts in some areas as they are swamped with motorists. Repair bills are topping £1,000 for some drivers.
This seems to point at a fairly localised batch of fuel
Petroleum Industry Association
How fuel can be contaminated
The UK Petroleum Industry Association said the problem could have arisen because of the way a single batch of fuel was blended or stored, and that petrol across the UK was generally not faulty.
Ray Holloway, of the Petrol Retailers Association, said garages had told him the problems may have been around for a week, so the exact cause might not be found.
"I've been in this industry for over 30 years and I don't remember anything like this happening before, and therefore to give you a cause is very difficult at this stage."