The firm, owned by the billionaire Issa brothers, said the move was to "ensure as many [of our] customers have access to vehicular fuel."
It comes as long queues formed at petrol stations around the county yesterday, amid fears of a fuel shortage.
A statement from EG Group said: "To ensure as many of our customers have access to vehicular fuel, we are restricting transactions to a maximum of £30 per customer on all of our grades.
"This is a company decision and our colleagues have been asked to stop the pump if you have exceeded this amount.
"We hope to return to normal service as soon as possible."
Pictures and videos across Lancashire yesterday revealed motorists continued to line up for fuel despite the government urging people not to panic buy.
"There is no shortage of fuel in the UK, and people should continue to buy fuel as normal," a Government spokeswoman said.
The rush was triggered by news that a small number of BP and Tesco petrol stations had been forced to close as a shortage of HGV drivers meant they could not be restocked in time.
Edmund King, president of breakdown and recovery service the AA, said that "there is no shortage of fuel and thousands of forecourts are operating normally with just a few suffering temporary supply chain problems."
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