Online travel agencies outperform airlines in terms of customer experience, a major contributor to the agencies' success in converting shoppers to customers, a website-tracking firm said Thursday.

Based on research with 2,000 consumers using the 16 leading travel and airline web sites, Keynote Systems Inc. found that the three top agency sites, Expedia, Orbitz and Travelocity, scored "significantly better" than any airline site, except Southwest, in customer satisfaction and customer conversion.

"Greater selection is a major inherent advantage for online travel agencies," Keynote analyst Bonny Brown said in a statement. "But online agencies are also creating a better overall online experience for customers and this is a significant contributor to the success of these sites over airline sites. The airlines are just not fully capitalizing on their loyalty programs and direct ties to the customer."

Low-cost carriers Southwest and JetBlue were exceptions to the rule, rating the best among other airline sites in terms of customer experience and conversion, Keynote said. Southwest, however, was the only airline site to drive bookings as effectively as the online agency sites.

"Airlines such as Southwest and JetBlue have demonstrated that airlines can successfully compete against online travel agencies," Brown said.

Keynote also found that 70 percent of consumers with online access say they book air travel online, compared with 25 percent who call airline customer service. Price is the most important consideration for 81 percent of consumers making a purchase, with 50 percent of consumers saying the ease-of-use of a website is also an important factor.