Surrey Police said it was investigating complaints from customers who reported fraudulent bank account activity after paying by chip-and-pin.
The garages involved are BP in Redhill, Shell in Leatherhead and Buckland, and Total at Tattenham Corner, Epsom.
Police said: "We are liaising with the banks and petrol stations concerned."
"It is very difficult to give precise numbers"
One was released without charge while the other is on police bail until 10 April pending further inquiries.
A Surrey Police spokeswoman said: "We have received a number of reports from people claiming their cards have been compromised.
"It is very difficult to give precise numbers of compromises as it is a complex and prolonged investigation."
Some of the transactions are said to have taken place as far back as last November.
The spokeswoman said customers' bank accounts had seen alleged fraudulent activity in countries as far afield as Pakistan and Canada.
The UK payments association, Apacs, recently released figures showing that counterfeit card fraud went up by 3% from 2005 to 2006, while fraud suffered abroad shot up by 43% in the same period.
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