ATLANTA/NEW YORK, March 11 (Reuters) – Demand for air travel among business customers is rising and major US airlines said on Tuesday they would consider charging additional fees while cutting costs to increase their profits.

Delta Air Lines, the world's largest carrier, said business trends were improving. Unit revenue in March would be up 16 percent, the company said.

United Airlines is ''clearly seeing signs of economic recovery and premium and corporate travelers returning,'' UAL Corp. Chief Financial Officer Kathryn Mikells told attendees at a J.P. Morgan conference.

''The return of higher quality traffic, combined with the significant reductions in capacity that we undertook in 2009, has really begun to improve our relative revenue results,'' Mikells said.

Traffic reports for the first two months of 2010 signal that demand is improving at major US airlines. Load factors, a measure of how full a plane is, were higher for the top six US airlines last month.

American Airlines parent AMR Corp expects unit revenue to be up 6.5 percent to 7.5 percent in the first quarter. Low-cost carrier Southwest Airlines said March bookings were ''very strong'' while rival  AirTran Holdings Inc. cited ''rapid'' improvement in yield trends.

''Things are moving in the right direction,'' said S&P analyst Jim Corridore, who has ''buy'' ratings on many airline companies' stocks. ''The airlines have really improved the supply-demand balance in terms of capacity, so pricing should go up on strengthening demand.''

Airlines should be able to raise fares this summer, Corridore said.

The Arca Airline index hit a two-year high in afternoon trading. American shares vaulted more than 11 percent before paring gains to rise 9 percent.

The airline industry cut back on the number of fare sales, which led to higher ticket prices, said US Airways Chief Operating Officer Robert Isom at the JP Morgan event.

Airline executives also reiterated the need for the industry to temper capacity increases as the industry recovers from high fuel prices in 2008 and a severe recession in 2009.

US airlines cut capacity nearly 7 percent in 2009, the deepest annual cut since 1942, according to the Air Transport Association. Airline executives said Tuesday they were not ready to put seats back into the market.

''There is no indication we should be adding capacity,'' American CEO Gerard Arpey told reporters at a conference in Washington. For American, he said, ''we've got to generate a lot more revenue.''