More airlines are moving toward credit and debit card transactions for onboard purchases.

Since most airlines are charging for food, alcoholic beverages and entertainment, and some charge for nonalcoholic beverages, you'll want to know the airline's payment policy before you board.

For many travelers who are used to relying on credit cards, this is good news because it eliminates the need for cash.

It also is more convenient since flight attendants can quickly swipe your card and you won't have to wait for change.

The airlines have found that they can make more money by using handheld credit-card machines because passengers tend to spend more when they use a credit card.

Onboard revenue will also grow as airlines charge for more items that used to be free.

Beginning Aug. 1, US Airways will charge $2 for nonalcoholic beverages (including water) in coach class, and alcoholic beverages will rise from $5 to $7 per drink.

Other carriers are charging $4 to $6 for alcohol, so don't be surprised if their rates inch up. Spirit already charges for all beverages, so US Airways is not the first to enter that territory.

The latest airline to join the cashless cabin is Alaska Airlines, which will stop accepting cash Aug. 5. To promote the change, the airline is offering 10 miles per dollar spent for travelers who charge their purchases with an Alaska Airlines Visa card. The offer is valid through Oct. 31.

Airlines that accept only credit cards include AirTran, Frontier, JetBlue, Midwest, Spirit and Virgin America.

American and Delta accept cash, credit cards and debit cards.

United recently finished a credit and debit card test phase on transcontinental flights, so it may be the next to switch to a cashless cabin.

Continental accepts cash onboard, but you can buy Continental Currency coupons at airport kiosks with a credit card before you board for $5 for one, $10 for two, $13 for three or $25 for six. Alcoholic drinks cost $5 or one coupon.

If you want to rent a headset, you may want to bring bills since they cost only $1 when you use cash, or else you can redeem one coupon. Continental still provides free meals.

US Airways doesn't have handheld credit-card equipment, so it doesn't take credit cards.

Northwest, Southwest and United are the other cash-only airlines.

Tom Parsons is publisher of Bestfares.com.