(FORTUNE Magazine) – Your workdays are longer, your stress is higher, and the demands at home don't get lighter. The need for an oasis is never so acute as it is in the airport, that never-never land that is neither home nor work. Even when your trip goes smoothly--when there are no equipment changes, when there are no weather delays, when a connecting flight isn't late in arriving--airports all too often are an endless series of intrusive flight announcements, broken pay phones, fast food, and too much time spent in those little plastic bucket seats by the gate.

The alternative: For about $200 a year, airport clubs deliver sanity and comfort to a surprisingly select number of harried business travelers who are willing to plunk down an annual membership fee. Once upon a not very long time ago, clubs were little more than superannuated frat houses where hard-drinking, heavy-smoking traveling salesmen swapped fish tales and flirted with the exceedingly rare women members. Today membership may be the single best investment frequent-flying executives can make to maintain their equanimity and competitive edge on the road.

The once sacred rations of free cocktails are mostly gone (only the Delta Crown Rooms and Northwest WorldClubs maintain the tradition at domestic clubs), and many clubs ban smoking. Now the clubs are airport-based remote offices that offer business travelers--men and women--a much needed refuge.

Even the most primitive airport club is now usually stocked with work desks, fax and copy machines, telephones and dataports, overnight-delivery drop boxes, and other business necessities. Concierge-like attendants secure boarding passes and seat assignments. Bigger clubs in the airline networks, like Northwest's sprawling Detroit facility and the huge Continental Presidents Club in Newark, boast fully equipped conference rooms, top-of-the-line Wintel personal computers, a spread of popular software, and laser printers. And, at a dozen major international airports--Seattle, Frankfurt, and Miami, to name three--American and United have built showers for travelers who hit the ground working.

What's driving the airlines to make these subtle but important changes are the new priorities of the customers. "If we had a club without telephones, members would go ballistic," says Georgene Ross, senior staff representative for airport services planning at United Airlines. "But I don't think many members would notice if we ever pulled the bar out of a club."

This attitude adjustment among business travelers hasn't gone unnoticed by the airlines. Despite the scarcity (and expense) of airport real estate, the nation's three largest carriers-- United, American, and Delta--have each added an average of three new clubs a year in the 1990s. United alone says it has invested about $70 million on airport club facilities this year. The payoff for the airlines? The 45 American Admirals Clubs are now "a healthy little profit center," says marketing manager Teresa Hanson. The airlines also are convinced that more, bigger, and better-equipped clubs will persuade at least a few first- and business-class travelers to throw additional flight segments their way.

But the real surprise about airport clubs is the number of business travelers who don't realize the comfort and productivity generated by an investment of a few hundred bucks. American and United both have about 250,000 paying members for their respective club networks, only about a hundredth of the number of members each airline claims for its free frequent-flier programs. "It's about money," explains Hanson. "Some business travelers say they won't join unless their company pays for the membership or they can add it to their expense account."

If you're one of those hard-nosed business travelers who haven't yet analyzed the added value of having a quiet place at the airport, consider this simple equation: If you fly ten times a year (one measure of what qualifies you as a "frequent flier") and spend an average of just one hour per round trip waiting at airports, a $200 annual club membership costs you just $20 per hour. Spend a total of 20 hours and the hourly cost of membership drops to just $10, a relative bargain.

Not ready for a commitment? Then try sampling an airport club. American Express Platinum card holders have free access to Continental's Presidents Clubs and Northwest WorldClubs on flight days whenever they're ticketed on those airlines. Many airlines quietly offer a day-pass program that, space allowing, permits one-time club use for a small fee (usually $25 to $50), and Continental has a 30-day pass for $30.

While the clubs may seem to be omnipresent--all the major airlines (except relentlessly no-frills Southwest) operate clubs, and all but one of the nation's 50 busiest airports have at least one club on the premises--don't be fooled. There are significant differences from network to network.

For instance, few airlines have reciprocal arrangements with one another; if you're stranded at an airport where your airline doesn't have a club, you're usually clubless. So consider enrolling in a network that has a multiclub presence at some of major hubs. There are six Delta Crown Room Clubs in Atlanta (Delta's primary hub), three in Dallas/Fort Worth, and two in Cincinnati. USAir maintains three clubs at its hubs in Pittsburgh and Charlotte, North Carolina. Continental has two Presidents Clubs at its Newark hub. Northwest has three clubs at its Detroit hub. TWA, whose network of aging Ambassadors Clubs has shrunk with the airline, nevertheless runs two clubs at both its hubs (in St. Louis and at New York's Kennedy airport). Even tiny America West operates two clubs in Phoenix, its hometown airport.

Fly so frequently that you can't match your travel patterns to one airport and one network of club lounges? Do yourself a favor: Join two clubs. You'll appreciate the wisdom of your decision the next time you've got six hours on your hand when an unexpected thunderstorm means you'll be stuck inside of the Mobile airport waiting for the next flight to Memphis.