There is little more frustrating than finding a low airfare on the Web and jumping through hoops to book it only to get a message late in the process that the fare is no longer available.
Each of the big three travel Web sites -- Expedia, Travelocity and Orbitz -- claims to have "real-time availability." What that means to the consumer depends on whom you talk to.
"The industry tends to use the term very loosely," says Ann Marie Razza, a product manager and airfare specialist with Orbitz.
Henry Harteveldt, principal analyst at Forrester Research in San Francisco, an independent technology research company, thinks the terminology isn't as important as the result of the traveler's efforts to book: "What really matters for the traveler is: Is the seat you want available?"
All three sites work with the same complex airfare information. The difference is how they manage that information.
There are three components of airfare information, and all are volatile. The first is flight schedule, which can change as often as three times a week. The second is fares and rules, which can change up to five times a day. The most changeable component is availability, which can vary by the minute. That last category is usually what causes fares to disappear.
For example, you find a fare for which only two seats remain, but you do not know that's the case. John Doe in Idaho may find the same fare at the same time and may want those two seats too. It is then a race to see who completes the booking first -- but you do not know that you and John are competing.
Adding to the confusion: Sites offer at least two ways to book flights. One is straightforward: a flight from here to there on a specific date.
The other way to book a flight allows more flexibility but does not reflect real-time availability. Harteveldt calls it "a little bit of dreaming."
If you fall into the dreaming category, be prepared to work your way through several searches before you can book the fare you want.
For a flexible search on Travelocity, you are presented with dates that qualify for the lowest fares. Remember, it's not the same as seats being available at those fares on those dates.
Using Travelocity's flexible option, I tried to book a $197 round-trip fare (excluding taxes and fees) on British Airways from Los Angeles to London. My preferred departure date, Dec. 3, qualified for the fare according to the calendar, but when I selected it, I got a message that "confirmed four alternate dates around your desired date." There was a big 'X' through Dec. 3.
I selected one of the alternate dates, which were outlined in green. The return flight required four attempts before I finally found a date in green -- a month and a half later, significantly longer than the weekend trip I had in mind.
On Expedia, the calendar contains the best domestic fares recently found by customer searches. But the fares on these calendars are not necessarily available when it's time to buy them in real time.
On Orbitz, consumers enter their criteria, then use its Flex Search tool. Orbitz then searches through its database, loaded with frequently refreshed, cached data, and displays a selection of fares in a matrix. When you choose one, Orbitz validates availability by linking directly with the airline system in real time.
Of the three sites, Orbitz may come closest to offering flexibility and real-time availability, but so far, like Expedia, it's only with domestic destinations.
"Orbitz has developed some sophisticated technology," Hart- eveldt says. "They've reinvented the way to get fares."
Orbitz's technology doesn't directly connect with the airlines' reservations systems when a consumer is browsing, so by the strictest definition it is not real time.
"We don't want to bombard the airline systems with too many customer requests," says Orbitz's Razza. "It would bring the airline systems to their knees."
Expedia, on the other hand, uses a Windows-based technology for its booking service that checks the airlines' systems from the first search.
"We ping the airline's reservation system directly for availability each time the consumer presses 'go,' " says Expedia spokeswoman Andrea Riggs. "It is called a 'seamless availability request.' "
Though Expedia's search may be in real time, it doesn't have the same flexibility as an Orbitz search. For more date options in Expedia, you must go outside the realm of real-time availability and to its calendars.
Travelocity also claims real-time availability but is a bit more equivocal than Expedia.
"Wherever possible, the fares are checked in real time," says Ginny Mahl, Travelocity director of air travel marketing. "Sometimes when there is a lot of shopping, like during the holiday season, the airline systems don't respond as quickly, and some airlines simply don't have the technology to respond."
That can require patience at the keyboard.
"When something happens, like the flight is not available, do the search again" and check a variety of sites, including the airlines' sites, Harteveldt says.
With millions searching for inexpensive tickets, the fare you see today might not be available at the moment. "If you see a good fare, buy it," Harteveldt says.
James Gilden can be contacted at www.theinternettraveler.com.