NEW YORK-US air­lines have used surg­ing oil prices to jus­ti­fy fare in­creas­es of up to $60 per tick­et since the start of the year. But the ris­ing cost of fu­el isn't the on­ly rea­son it's get­ting more dif­fi­cult to find cheap fares."This is prob­a­bly go­ing to be the worst year we have seen in 10 years in terms of find­ing bar­gains," says Tom Par­sons of Best­Fares.com, a web­site for trav­el deals.Even be­fore tur­moil in the Mid­dle East drove oil prices high­er, air­fares were climb­ing. The av­er­age cost of a round-trip tick­et on a US air­line was $360 be­fore tax­es at the start of 2011, a 9 per­cent in­crease from the pre­vi­ous year. By sum­mer that fig­ure could reach $430, says Robert Herb­st, an in­de­pen­dent air­line an­a­lyst.

Some high-traf­fic busi­ness and leisure routes, such as New York to Los An­ge­les, will see large hikes, Par­sons says. The cheap­est fare be­tween those cities last Ju­ly was $382. This year, it's $544. Par­sons notes a hand­ful of do­mes­tic routes, such as Dal­las to San Fran­cis­co, are down thanks to new com­pe­ti­tion.

Air­lines have the up­per hand on prices for sev­er­al rea­sons:

• The im­prov­ing econ­o­my. Busi­ness trav­ellers are ex­pect­ed to take 441 mil­lion trips this year, a 3 per cent in­crease from 2010. As a re­sult, air­lines are re­serv­ing more seats for pricey last-minute book­ings. That leaves few­er cheap fares for leisure trav­el­ers, who tend to book fur­ther in ad­vance.

• Few­er seats. Dur­ing the re­ces­sion, air­lines re­duced the num­ber of routes and planes they fly. As trav­el de­mand picks up, this shrunk­en sup­ply of seats al­lows the in­dus­try to charge more. Planes are 82 per­cent full on av­er­age, com­pared with 70 per­cent full be­fore the re­ces­sion hit in late 2007.

• Con­sol­i­da­tion. Six air­lines have com­bined in­to just three over the past 14 months-Delta and North­west, Con­ti­nen­tal and Unit­ed, Mid­west and Fron­tier-leav­ing bar­gain-hunters with few­er choic­es.

It isn't just the base fare get­ting more ex­pen­sive. Check­ing bags, re­serv­ing an aisle seat and oth­er ser­vices are no longer uni­ver­sal­ly free. An­oth­er change work­ing against leisure trav­el­ers is the bud­ding dis­pute be­tween air­lines and on­line trav­el sites. The air­lines want to pay the sites low­er com­mis­sions for each tick­et pur­chased. The re­sult for fliers: Not all avail­able flights can be found on some sites. For in­stance, Or­b­itz, Ex­pe­dia and Hotwire no longer list Amer­i­can Air­lines flights.