WASHINGTON – A new NACS study found that drivers are paying 6 to 10 cents a gallon in hidden bank fees every time they gas up.

To make matters worse, the banks' swipe fee goes up inexorably with the price of gas, even though your bank is doing nothing extra to process your debit or credit card transaction.

Swipe fees have grown to be a convenience retailer’s largest operating expense after labor — more than rent, more than utilities. Convenience stores paid more than $11 billion in card fees last year, a jump of almost 25% and an amount almost 90% greater than their profits.

"These fees have come to be a tremendous burden on convenience stories, most of which are run by small business people," said Lyle Beckwith, NACS senior vice president of government relations. "In many cases, the banks are profiting more from the sale of gas than our members."

As gas goes to $4 in some markets, the bank's average cut of swipe fees alone increases to 7 cents, if you pay with a debit card and up to 10 cents with a credit card. Consumers pay the extra money even if they pay cash because the credit card companies' rules push the merchant to pass along the costs to everyone — not just customers who pay with plastic.

The study also found that gas prices increased 80% between 2004 and 2011. Card fees rose 180%. In other words, even when gas prices level off, the bank fees continue to rise.

Because credit-card fees are fixed in secret by a duopoly of MasterCard and Visa, they always are on the increase, to the point where they are now the highest in the industrialized world.

Read the full report, "Hidden Bank Fees Siphon Money from Customers and Merchants at the Pump.”