CHICAGO (CBS) – The war brewing between the big airlines and online travel websites is expected to make comparison-shopping more difficult for consumers.

It started with American Airlines and Orbitz. Then Orbitz competitor Expedia dumped American. Now Delta flights are no longer sold on three travel sites as well.

The journey for many fliers actually begins on the World Wide Web. Centralized online websites allow consumers to find the best fare.

American ended its relationship with Expedia in part because the website wouldn’t list the array of options for more room or refundability that the airline markets on its own website.

With bargain-hungry travelers, the major airlines tend to lose out to low-cost carriers when prices are listed side by side on the travel websites. Analysts believe more airlines could follow American’s flight plan.

“Immediately, this is a bit of a downside to the consumer. It adds to the search cost. It makes that one-stop-shopping more difficult,” says Joe Schwieterman, a DePaul University transportation expert.

CBS 2 did its own experiment, checking two travel websites and American’s web site to find the best fares for a mid-week flight from Chicago to Denver; a longer-distance flight from Chicago to Los Angeles; and an overseas flight from Chicago to Rome.

To confirm the lowest roundtrip fares – the $180 cost from Chicago to Denver, for example – all had to be checked, which was time-consuming. The process will only become lengthier if other airlines follow American’s lead and leave the centralized travel sites.

“These big web sites have a future, but they’re going to have to diversify from just comparison-shopping on airlines,” Schwieterman said.