Delta Air Lines Inc., the third-largest U.S. carrier, is adding fuel surcharges of as much as $50 for frequent-flier tickets to blunt this year's 42 percent surge in jet-fuel prices.

Delta joins US Airways Group Inc. and American Airlines in charging to redeem the rewards, a new source of income as carriers try to stem widening losses. Taxes, security fees and airport landing charges collected by many airlines on frequent-flier travel must be passed on to government agencies.

Delta's award tickets for U.S. and Canada travel will have a $25 surcharge starting Aug. 15, and international tickets will be $50, the Atlanta-based airline said Friday in a statement.

Fuel costs are causing "considerable financial stress" on Delta, Jeff Robertson, managing director of the airline's SkyMiles frequent-flier program, said in the statement. Delta will re-evaluate the fee should fuel prices decline, he said.

Delta had 41 million SkyMiles members as of February, according to WebFlyer.com.