How much are people willing to pay to fly?

The cost to fly is climbing fast, and the trend could extend well beyond the peak summer travel season.

So far this year, travelers have been hit with nine fare increases, the latest coming Friday as Northwest Airlines and most other carriers matched the 3- to 5-percent rise initiated Thursday by United Airlines.

Short-lived fare increases have long been common, but this year is different, with managements desperate to compensate for oil prices that have risen far beyond anything they anticipated.

Delta Air Lines Chief Executive Officer Richard Anderson, who this month began what many observers believe could be a major consolidation of the industry by proposing a merger with Northwest, said last week that fare increases of another 15 to 20 percent are needed to keep airlines solvent.

"I take the Delta CEO at his word and I think fares will be up well over 20 percent by the end of May," said Rick Seaney of the ticket-research site FareCompare.com. "We're on pace for just under 40 increases for the year, which is absolutely crazy."

In years past, six to 12 fare increases were more typical, he added.

The fare increases will hit hardest on routes with little competition, including those in and out of small airports. Coupled with other new or rising fees -- including $25 for a second checked bag at most airlines, and $150 for a ticket change at United, up from $100 -- industry observers expect to soon see a change in travel patterns, with some people giving up on discretionary travel plans altogether.

Travelers in for a shock

Don't expect that to mean less-crowded planes this summer, however.

Bill Swelbar, an airline expert at the Massachusetts Institute of Technology, said many people taking vacation trips between now and the fall will be traveling on tickets booked when "oil prices were $30 a barrel ago." That means a huge gap between what those customers paid to travel versus what it will cost the airlines to get them to their destinations.

Those same passengers could be in for a shock, though, when they go to book trips for fall and winter. Rather than the usual retreat in fare prices seen for that time of year, they could find themselves paying steep increases over what it cost a year ago to take a ski trip, bring a son home for a weekend from college, or visit relatives.

The sticker shock will force travelers to be more creative, said Tom Parsons, CEO of Bestfares.com, a discount travel site.

People might still find coast-to-coast roundtrips for $200 on occasion, or Minneapolis to London for $600, Parsons said. But flying in or out of destinations served by just one or two carriers will be a different story.

He gave a couple of examples, based on Northwest fares as of Friday afternoon.

The cheapest direct fare at that time for Fargo to Chicago roundtrip was $656. But he could book connecting flights -- Fargo to Minneapolis and Minneapolis to Chicago -- roundtrip for a total of $356.

Similarly, Northwest's cheapest fare for Minneapolis to Key West was $866. But Minneapolis to Miami was $258, a $600 savings for someone willing to drive the rest of the way. For a family of four, that adds up to more than $2,400.

"For that [difference], I'd say, 'Kids, we're going to have a nice, scenic three-hour drive,'" Parsons said.

With airlines flying full planes and still losing money, their long-term survival strategy is to merge. Short-term it's to economize on fuel by flying less.

Carriers are paying about 50 percent more for fuel now than at this time last year, and Delta and Northwest together had a loss approaching $500 million from their operations for the first three months of 2008.

A number of airlines have already announced plans to substantially cut their fall flight schedules, with Northwest saying it will pare more than 12 percent of its flights. With fewer planes taking off, that means less competition to fill seats, and fewer fares at budget prices.

"So now they don't have to worry about filling planes, but how much people are willing to pay," Seaney said. "They can't wrack up those kinds of losses and survive."

Liz Fedor contributed to this report H.J. Cummins • 612-673-4671