In the beginning, choosing and using a frequent-flier program was a straightforward procedure. First, join the mileage program of the airline which you find yourself naturally gravitating toward — typically the carrier which offers the best lineup of flights from your hometown airport. Then, maximize earnings by flying the host airline and other program partners whenever possible.

But as the airlines expanded their partner rosters to include other airlines — sometimes even their own competitors — the choice of program was complicated by an overabundance of options.

Consider Alaska Airlines' Mileage Plan program as an example. While Alaska's route network is principally concentrated in the Pacific Northwest, members of Mileage Plan can earn and redeem miles for flights not only on Alaska but for flights on American, Continental, Delta and Northwest. And those are just Alaska's domestic partnerships. Among the non-U.S. carriers on the partner roster: Air France, British Airways, Cathay Pacific, KLM, LAN Chile and Qantas.

So while the airline itself operates within a geographically circumscribed area, Alaska's mileage program knows no such bounds. A traveler who lives outside Alaska's own service area, and never earns miles for Alaska flights, could nevertheless be well served by Alaska's mileage program by earning and redeeming miles exclusively on the airline's partners.

GOING GLOBAL

The situation was further complicated when, in 1993, the larger airlines began grouping themselves into global alliances. The core concept behind the alliances was that airlines could realize many of the benefits of merging, without incurring the associated expenses and government-imposed restrictions, by forming deep and wide relationships with other airlines.

In particular, groups of affiliated airlines could link their schedules, coordinate their service standards and share airport terminals, in the process creating global route networks that would increase convenience for the traveling public and profitability for the airlines. A key component of such networking is the integration of the participating airlines' frequent-flier programs.

In theory, a traveler can get to most any destination on the globe by combining flights of alliance carriers. And because the airlines have coordinated their schedules and consolidated their gates into common terminals, the trip will be shorter (faster flight connections) and more convenient (no terminal transfers required).

In between connecting flights, travelers who have frequent-flier program elite status or who are flying on more expensive tickets would have access to the alliance partners' airport lounges. The customer will earn miles — and not just base miles but elite-qualifying miles — for flights on each alliance partner. And elite members of the participating airlines' programs receive special recognition and benefits when flying on any carrier within the alliance network.

THREE ALLIANCES

Today, the majority of the world's full-service airlines participate in one of the three global airline alliances: oneworld, SkyTeam and the Star Alliance.

The Star Alliance, established in 1997, is the oldest alliance to survive in its original form. And by most measures, it is the largest. Star partners include Air Canada, Air New Zealand, ANA, Asiana, Austrian, bmi, LOT Polish Airlines, Lufthansa, Scandinavian Airlines, Singapore Airlines, South African Airways, SWISS, TAP Portugal, THAI, United and US Airways. The 16 Star carriers together serve 855 airports in 155 countries and host 650 airport lounges.

The oneworld group comprises 10 airlines: American, British Airways, Cathay Pacific, Finnair, Iberia, JAL, LAN Airlines, Malev, Qantas and Royal Jordanian. In total, the group flies to 692 cities in 142 countries and offers 392 airport lounges.

And finally, SkyTeam's combination of Aeroflot, Aeroméxico, Air France, Alitalia, Continental, CSA, Delta, KLM, Korean and Northwest serves 728 airports in 149 countries and has a combined 400 airport lounges.

MORE BENEFICIAL NOW

The consumer benefits of alliances once were limited to travelers flying internationally, who could take advantage of the optimized flight connections among the participating airlines. That's because, in the alliances' early years, the tendency was to feature just one airline for each geographic region. So for the United States, oneworld was represented by American, SkyTeam by Delta, and Star by United. As a result, alliance partnerships weren't a meaningful consideration for those who mainly traveled domestically. But while American remains the sole U.S. carrier in oneworld, SkyTeam has added Continental and Northwest to its roster, and Star has added US Airways.

So today, a domestic traveler considering the benefits of joining Continental's OnePass program would do well to factor in the opportunity to earn elite-qualifying miles when flying on Delta and Northwest. And for the first time in the evolution of the alliances, Star now provides alliance benefits to travelers flying on a discount carrier, US Airways.

For travelers currently considering their frequent-flier program options, it's now more about choosing an airline alliance than it is about picking a single airline. That requires more analysis of more variables. But the enhanced benefits available from an alliance that dovetails with a flier's needs more than justify the extra effort.

Reach Tim Winship at questions@frequentflier.com