Delta Air Lines Inc., the nation's third-largest carrier, will double its charge for checking a second bag on a domestic flight as part of a set of fee increases to help offset the high cost of fuel.

The Atlanta-based carrier said Tuesday that the changes will apply to customers who purchase a ticket on or after Thursday for travel on or after Aug. 5.

Fee changes include an increase from $25 to $50 to check a second bag for domestic travel. Fees for specialty items that require special handling, such as surfboards or ski equipment, will increase on domestic and international flights, Delta said.

First Class, BusinessElite and Medallion customers will still be able to check up to three bags at no charge, the airline said.

Delta said that as fuel costs remain high, it believes revising its fee structure for excess bags and specialty items is essential to generate the necessary revenues to offset its higher costs.

Delta currently does not charge passengers for checking a first bag on domestic flights. It has said it is studying a decision by several other major carriers to impose that fee.

Delta customers checking bags on international flights can check a first and second bag at no charge.

Fees are for each extra bag, each way.

Delta officials said less than 20 percent of its passengers check more than one bag.

The fee for checking a third bag on a domestic flight will increase from $80 to $125, while the fee for checking a bag that is between 51 and 70 pounds on a domestic flight will rise from $80 to $90. On any flight checking a bag that is 62 inches to 80 inches of the total of its length plus its width plus its height will rise from $150 to $175.

Delta warned on its Web site that if a customer has an extra piece of baggage that goes over the weight limit and the size limit, the passenger will be charged three times -- once for the extra bag, once for going over the size limit and once for going over the weight limit.

The airline said it accepts up to 10 checked bags on Delta mainline flights and four checked bags on Delta Connection carriers.

It said a $175 charge per item applies to media representatives carrying camera, film, video tape, lighting, or sound equipment.

Delta announced April 14 that it will acquire Eagan, Minn.-based Northwest Airlines Corp. in a stock-swap deal that would create the world's largest carrier in terms of traffic. The deal is subject to shareholder and regulatory approval.