ATLANTA — 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.

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.

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