July 29 (Bloomberg) -- Delta Air Lines Inc. doubled the fee for checking a second bag on domestic flights to $50 each way, the most of any of the six biggest U.S. carriers, to defray record spending on jet fuel.

Today's move raises the bar again for baggage charges as the industry struggles with losses. United Airlines led its large peers in adopting a $25 second-bag fee on Feb. 4, and American Airlines went a step further in May by announcing a $15 charge for the first piece of luggage.

Delta, the third-biggest U.S. airline, said the first checked bag on U.S. flights will still be free, and international travelers can still check two bags without charge.

``They're trying to have the second-bag charge subsidize keeping the first bag free,'' said Jay Sorensen, a former marketing director at Midwest Air Group Inc. who now runs Ideaworks, an aviation consulting firm in Shorewood, Wisconsin.

Delta's second-bag fee tops the $25 at AMR Corp.'s American, UAL Corp.'s United, Continental Airlines Inc. and Northwest Airlines Corp., which round out the five biggest full- fare carriers. Southwest Airlines Co., the largest discounter and No. 5 overall by traffic, doesn't charge for the first two bags.

United and Northwest are among the airlines that joined American in charging $15 for the first checked bag.

Fewer than 20 percent of all Delta passengers check a second bag, spokeswoman Betsy Talton said. She declined to say how much additional revenue the new fees will generate.

Fallout From Fuel

Jet-fuel prices have jumped 66 percent in the past year, to $3.63 a gallon today, and closed at a record $4.36 a gallon on July 3. Fuel has surpassed labor as the biggest cost for most carriers and sent all the full-fare airlines including Delta to second-quarter net losses.

Delta's charge for checking a third piece of baggage in the U.S., the Virgin Islands and Puerto Rico is increasing to $125, from $80 previously. Four bags or more will cost $200 each.

On international flights, the third bag will cost $200, up from $150 previously. The fourth and fifth bag will be $350, with any additional bags costing $600.

``People are going to become much more aware of what they pack,'' Sorensen said. ``Delta is trying to create a distinction from the other carriers by keeping the first bag free.''

The higher fees apply to tickets bought on or after July 31, for travel on or after Aug. 5, Delta said.

Delta in April agreed to buy Northwest to form the world's largest carrier. Northwest isn't considering changing its luggage fees, spokeswoman Michelle Aguayo-Shannon said.

Delta rose $1.01, or 15 percent, to $7.91 at 4:15 p.m. in New York Stock Exchange composite trading. The shares have fallen 47 percent this year.

To contact the reporter on this story: Mary Jane Credeur in Atlanta at mcredeur@bloomberg.net.

Last Updated: July 29, 2008 17:51 EDT