Customers at a Tesco forecourt in south Wales were given short fuel measures over a period of eight months, it has emerged.
The supermarket giant, which admitted delivering short measure fuel and using unjust measuring equipment on at least six occasions between October 2007 and July 2008, was fined £18,000 with £6,500 costs.
More than nine million litres of fuel was sold to customers at Tesco's Ystrad Mynach filling station during the period, Caerphilly Magistrates' Court heard.
The problem, which was caused by an incorrect modification to the chip and pin readers, only came to light following a routine inspection by Caerphilly County Borough Council trading standards officers.
All grades of fuel on three of the petrol station's six fuel pumps were affected, causing a total loss to customers of an estimated 168,000 litres of fuel.
A Tesco spokesman said: "We have since contacted many thousands of customers to apologise for our mistake and offer a refund or, if they prefer, a donation to a local charity. Tesco will also make sure that the total refunds and charity donations add up to more than twice as much as the original overcharges caused by the fault at the pumps."
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