CHARLOTTE, N.C. -- Some drivers paying for gas with a debit card are experiencing a different kind of pain at the pump.

Gas stations concerned about collecting on automated debit-card transactions are freezing large amounts of money in consumers' checking accounts, causing financial headaches for drivers who carry low balances.

When a consumer swipes a card at a gas pump, most gas stations freeze $1 as a confirmation that a valid checking account exists. That hold usually lasts for a few hours, but can stretch for a couple of days. The station later debits the actual amount of the gas purchased from the account.

But as gas prices soar to record heights and fill-ups reach into triple digits, some stations are freezing much higher amounts.

The consumer protection division of the North Carolina Attorney General's Office has received more complaints this year about the practice, said spokeswoman Jennifer Canada.

The office doesn't keep statistics on the specific complaint, but "as gas prices rise, gas stations tend to do this more," she said.

For instance, one consumer reported that she purchased $25 of gas using her debit card at a Shell station in Fort Mill, S.C. But she had $90 frozen in her checking account for several hours, along with the $25 for the purchase.

The manager of the station did not immediately return a message. And several other managers reached at various gas stations said they didn't know what amounts were being held or how it was determined.

Hotels have been placing extra holds on debit and credit cards for years in case customers run up extra expenses before checking out, such as for telephone calls, minibar items or other services.

But it has been happening at gas stations because some fear banks won't cover increasingly large gas purchases if the money ends up not being in a consumer's checking account, said Red Gillen, an analyst with Celent, a Boston-based financial services research firm.

"Because there's a time lag between pumping and paying, there's a lot of money at risk. You're going to see more and more gas stations doing this," he said.

The hold policies can cause financial headaches for consumers in several ways, said Nathan Tothrow, director of marketing for Charlotte Metro Credit Union:

A debit-card transaction might be rejected even though drivers have enough money in their accounts for the gas they want to purchase.

"They have enough money for the gas, but not for the hold," he said.

The holds can tie up cash that can't be used for at least a few hours. Unsuspecting consumers might have other transactions declined because the holds are in place.

And there's a danger that the holds can stay on for longer than a few hours, causing other transactions to cause an account to be overdrawn, triggering fees.

Mr. Tothrow said the credit union had received complaints about excessive holds. The bank investigated and found several gas stations were freezing $75 and $90. Most still froze only $1, he said.

"For a lot of folks, a $90 unexpected hold can cause a problem," he said.