This year, travel purchases made on-line will reach nearly $2 billion, according to the Travel Industry Association of America. Trouble is, many Internet shoppers are overpaying for their plane tickets-- although electronic wizardry is impressive, it's still no substitute for a tuned-in travel agent, one with a bag of tricks the Web sites haven't heard of. And we're not talking about "hidden-city tickets," "throwaway ticketing," or back-to-back Super Savers-- dodges that the airlines have clearly ruled verboten. These are legitimate sleights that help you fly more cheaply.

1. SPLIT-CITY FARES What's the lowest round-trip fare between Minneapolis and Detroit that doesn't require a Saturday-night stay?Not the $940 "walk-up" price offered by the typical travel Web site or airline. A smart agent always checks to see whether writing two separate round-trip tickets (on different airlines, if necessary), with a stopover, makes for a better deal. Sure enough, you can get the best fare with two round-trips: one from Minneapolis to Chicago's Midway Airport, then another from Midway to Detroit. Total cost: $195.

2. SPLIT FARES (INTERNATIONAL) For a "split ticket," a travel agent issues a one-way business-type ticket (full coach, or business- or first-class) from the United States to a foreign destination in dollars and a second ticket back in the other currency, often saving a lot of money. It works only to some destinations-- and only on full-fare tickets-- but when it does it's very worthwhile. New York to Nairobi is $6,376 round-trip in business class if booked as one ticket; the same route is $3,183 going and $2,003 coming back when booked as two. Savings: almost $1,200.

3. CODE SHARING When one airline buys seats on another and sells them to the public as if they were its own, the practice is called code sharing, and it's tricky business. "Book a code-shared flight on the Internet and you might not realize that two airlines are involved, and possibly selling the same seat at vastly different prices," says Terry Trippler, publisher of "For example, American might sell a Boston-Johannesburg fare on South African Airways for a thousand dollars more than South African charges for the same seat." Always check all airlines that fly to a destination.

4. ADD-ON FARES Since tickets are often priced by what's called the "common-rated" method, you can sometimes add on a free segment. For example, New York-Paris-New York and New York-Paris-New York-Boston are both $1,513 at full coach fare. At no extra charge, you can add to the end of your trip the New York-Boston one-way that would normally cost $200, to be used anytime within a year (the fare must allow a stopover). Certain international tickets also allow you to add on other domestic flights, which can be used separately, for hundreds less than what you'd pay if you bought them on their own.

5. LEGAL BACK-TO-BACKS We all know that back-to-back ticketing (buying two round-trip tickets with Saturday-night stays and mixing and matching the legs) is against airline rules, right?But a smart travel agent knows how to do it legally. Example: You fly from Chicago to New York frequently and you don't want to stay over a Saturday night. You buy your first ticket as a one-way, Chicago-New York. Then add as many New York-Chicago-New York excursion fares as you require. For the last leg, you again buy a one-way ticket, this time New York-Chicago. Since you're not using any tickets out of chronological order, the airlines won't ground you.

6. TICKET VOIDS Let's say you purchase a non-refundable ticket and then change your mind. If you booked it with an airline, you're out of luck. But a travel agent can usually void the ticket through the end of the week in which it is bought. "Travel agents have some flexibility in reporting when a ticket was sold," one agent admits.

Someday, perhaps, travel Web sites will be able to do all this and more. Until then, however, don't fire your travel agent. The tricky part, of course, is finding a great agent.