With American Airlines in a tiff with major online travel agencies and Delta Air Lines blocking its flights from three smaller sites, fliers may need to tap the keyboard a few extra times to compare fares.

Delta quietly dropped its flight listings from online travel agencies Cheapoair.com, OneTravel.com and Bookit.com in December. In a much bolder move, American took on the biggy Orbitz when it failed to renew its contract, effectively blocking listings of its flights on that site. Expedia, in a show of support, dropped American flights from its main search results. Late last week, Sabre Holdings, the company that owns Travelocity, joined the fray by announcing it would not renew its contract with American in August.

For the time being, Priceline and Travelocity, plus a host of other sites, still list American and Delta flights in their search results. But if the snit between airlines and online agencies intensifies, a good bet for a comprehensive search will be aggregator sites. These search a myriad of travel providers -- from online agencies such as Orbitz to airline websites -- to find the best deals. When shoppers click on a selection, they are sent for booking to the originating site, which is often an airline's. Kayak.com and Bing Travel (at bing.com/travel) are two prominent aggregators.

Southwest Airlines and Sun Country Airlines, which have never appeared in listings of online agencies, require visits to their sites to check prices. That's just the kind of click-to-compare that travelers might need to get used to. Either that, or go with an old-fashioned aggregator with access to all airlines: a real live travel agent.