Most people have noticed that the price of gas is creeping up again. With the national average at $3.927 per gallon for regular gas, consumers are paying nearly 16 cents more per gallon than they did a year ago.

While some of that increase can be attributed to higher oil prices, the National Association of Convenience Stores (NACS) has discovered that swipe fees from credit and debit cards have also tacked on upwards of ten cents to every gallon of gas.

In its new report "Customer Card Fees: Hidden Bank Fees Siphon Money from Customers and Merchants at the Pump," the NACS found that these fees may cost the average driver over $30 a year.

When a consumer buys any purchase with a credit or debit card, he incurs a number of fees. The bank that issued the card charges the retailer an interchange fee for accepting the card. The retailer's bank charges the retailer a fee for processing the card transaction. The card network--Visa, MasterCard, American Express or Discover--also charges a fee.

Swipe fees also vary by the type of credit card. Generally, banks charge higher rates for rewards cards versus non-rewards cards. However, retailers have no idea what the rate is for each card it accepts. If the card is branded with a network the retailer accepts, such as Visa or MasterCard, the retailer has to accept all cards with that network brand, no matter what the interchange fee is.

Also, if a card is used in conjunction with a fraudulent purchase, the consumer doesn't have to pay for it, but the retailer often ends up paying a good portion of that loss.

For convenience store owners, who are typically small business owners, the fees have become an increasingly difficult cost on their balance sheet. For these businesspeople, fees to banks and card networks are the largest store cost after labor. Last year, convenience stores paid over $11 billion in card fees, an increase of nearly 25 percent over the previous year.

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

To make up for all of these fees, retailers pass the costs onto customers through higher product prices, so no matter whether you pay with cash or credit, you're paying extra to cover the cost of the swipe fees. The NACS estimates that the average family spends an additional $400 a year to cover the cost of swipe fees on all types of purchases.

In the case of gas purchases, every time a card is used, retailers pay both a flat fee and a variable fee that increases along with the transaction cost. As gas nears $4 a gallon, those fees add up to about seven cents per gallon for card purchases. Because debit and credit card swipe fees vary, for credit card purchases, the NACS says the fees can run nearly ten cents per gallon for credit card purchases.

Ironically, the NACS conducted a separate survey earlier this year on consumer behavior and gas prices and found that 14 percent of consumers would drive five minutes out of their way to save a penny per gallon. If the savings were five cents a gallon, 71 percent would drive five minutes out their way to save that money. 47 percent would drive ten minutes out of the way.

While "pay at the pump" makes life easier for consumers, as interchange fees continue to rise and be part of the factor of doing business, they will have to pay for that convenience.