Supermarkets have promised to pay for repairs to cars damaged by a batch of faulty petrol sold in stores across parts of the South East of England.
Tesco said all affected stores have been refuelled
Tesco and Morrisons have asked drivers who suffered problems after buying affected petrol to contact them.
Tesco has printed a full-page apology in several newspapers, saying stores have been refuelled.
Under the Sale of Goods Act 1979 motorists can claim for the petrol, any repairs and "consequential" losses.
Tests on samples of unleaded petrol from a storage facility in Essex found it to be contaminated with silicon, which may indicate the presence of silicone - often added to diesel.
Thousands of drivers last week reported engine trouble and breakdowns after filling up with unleaded petrol from a number of retailers, including Tesco and Morrisons supermarkets.
SILICON & SILICONE
Silicon is a chemical element - symbol 'Si'
Silicone is a chemical compound containing silicon and oxygen
Silicone can take solid or liquid form and is used as a lubricant and insulator
When silicon is found by tests on petrol it may indicate the presence of silicone
The Tesco advertisement appears in a number of papers under the headline: "Tesco petrol. It's back to normal and we're sorry."
It says "we'd like to pay for the repairs" and carries a telephone number - 0800 028 6428 - for customers to obtain further information and advice.
Motorists will be asked to send in receipts for the faulty petrol bought from Tesco and any car repairs carried out as a result of using it.
'Reasonable' repair refunded
A Tesco spokeswoman said if people did not have receipts they should call the advice line anyway because each case would be considered individually.
"Give us as much information as you can. A bank statement or credit card statement would be worth sending," she said.
"We will refund any reasonable costs of having the car repaired as a direct result of Tesco fuel."
A Morrisons spokesman said they would also refund petrol costs and repairs and said anyone who did not have receipts would be "supported".
He said customers wishing to make a claim should call 0845 611 6111.
"We have clearly sold contaminated fuel to customers. If people haven't got the receipts we will try to support that."
A spokesman for the consumer advice service Consumer Direct said: "We are advising people that they might be able to make a claim.
"The contract they had was with themselves and the organisation they bought the fuel from.
Tesco: 0800 028 6428
Morrisons: 0845 611 6111
"If they can prove the fuel was the cause of the fault they could claim for the petrol they bought, reasonable repairs to their cars and compensation for consequential losses incurred such as alternative arrangements they made."
The contaminated fuel was eventually traced back to four tanks at a Vopak storage facility in West Thurrock, which fuel supplier Harvest Energy said contained "unusually high levels of silicon".
Harvest Energy shares tank facilities at the depot with another oil company, Greenergy, which supplies both Tesco and Morrisons.
In a statement, Greenergy said a component understood to have been used by Harvest Energy in the production of unleaded petrol had tested positive for excess levels of silicon.