SOUTHFIELD, Michigan (Bloomberg) - UAL Corp.'s United Airlines raised its round-trip fuel surcharge by as much as $20, the second fare increase in a week, to help blunt record costs.

United boosted the surcharge by $20 round trip in markets that already had a fuel fee, spokeswoman Robin Urbanski said in an interview.

A $10 round-trip surcharge was added in markets where no fee had been in effect, she said.

The increase marks the 12th time this year that US airlines have tried to boost prices, with seven of the increases successful, Rick Seaney of fare tracker FareCompare.com said in an e-mail yesterday.

The move covers most of United's route system and applies to business and leisure travelers, Mr. Seaney said.

The Chicago-based carrier and other airlines are coping with record jet-fuel expenses and a slowing US economy. Crude oil selling for $100 a barrel or more will add an extra $2 billion in fuel costs this year, Mr. Urbanski said.

Crude oil, used to make jet fuel, topped $114 a barrel yesterday, the highest since futures began trading on the New York Mercantile Exchange in 1983.

Jet fuel for immediate delivery in New York Harbour has climbed about 80 percent in the past year.

UAL climbed 54 cents, or 2.4 percent, to $22.86 at 4pm in Nasdaq Stock Market composite trading.