Flying as a courier can reduce air costs to 50 percent to 85 percent below the lowest excursion fare, according to The Wall Street Journal.

Courier companies are the clearinghouses of the express shipping business. They handle the small quantities of overnight freight that the big shipping companies, like Fed Ex, UPS and DHL, don't want. Courier services deliver at least a few items every day to the cities they specialize in.

Courier travel opportunities have increased dramatically in the past 20 years as business depends more and more each year on guaranteed overnight shipping.

According to U.S. News & World Report, about 25,000 courier flights depart American cities each year. Similar patterns exist in Europe and the Pacific Rim, so the true number of courier opportunities in a given year may approach 100,000 flights.

It works like this: Air couriers secure bargain-basement roundtrip airfares by escorting shipping documents on international flights for legitimate air cargo/courier companies. The trade-off is that the couriers have to give up their baggage allowance and take only a carry-on.

The courier company uses the checked-luggage space for high-priority documents and articles that would be more expensive and likely delayed in Customs if shipped as cargo. At the end of the flight, the courier hands over the document pouch to a company representative and is on his own until the return flight.

The courier system was introduced after World War II when giant freight forwarder DHL calculated that it could fly time-sensitive material less expensively as checked luggage rather than as air cargo. Federal Express pioneered in 1971 with overnight mail and its own airplanes.

The need for speedy delivery gave rise to express courier companies that fly out of major U.S. Mainland cities. These firms serve as contract agents for the big cargo companies or serve their less-popular routes. The rationale is that escorted passenger baggage passes through Customs faster than ordinary freight which may languish, uncleared, for days at airports.

The courier companies buy commercial airline seats en masse months in advance at a huge discount. They, in turn, typically charge the courier-traveler much less for the ticket than they paid but make a profit on the delivery. Courier tickets require you to travel alone, to book at least 30 days in advance or, more commonly, be available at the very last minute, and take only one carry-on bag.

Airfare discounts for a courier are influenced by season and demand. (Couriers are usually permitted to stay from a week to 30 days at the destination and possibly could be engaged for duties on the return flight.) North American cities with daily departures include New York, Newark, Chicago, Washington, D.C., Miami, San Francisco and Los Angeles. International airports at Detroit, Ho-nolulu, Atlanta, Toronto, Montreal and Vancouver offer sporadic departures on courier flights. Common overseas destinations include Amsterdam, Johannesburg, London, Paris, Bangkok, Beijing, Hong Kong, Manila, Seoul, Singapore, Tokyo, Buenos Aires, Mexico City, Montevideo, Quito and Rio de Janeiro.

Requirements to be a freelance air courier include being 21, holding a valid passport, presenting a neat, clean-cut appearance and not having a felony record. You also need to be adventurous and flexible.

Information about courier flights is through membership in the International Association of Air Travel Couriers, www .courier.org. The association was founded in 1989 as a clearinghouse for consumers who want to travel as couriers to foreign destinations. It claims to track every courier company — some 200 plus — in the world and posts online twice-daily courier flight bulletins, available for a $45 annual fee, which also includes a bi-monthly subscription to Shoestring Traveler magazine featuring firsthand courier trip reports.

Its competitors — Courier Travel, www.couriertravel.org, and Air Courier Association, www.aircourier.org — offer members extensive listings of courier deals and standby specials as well as discounted negotiated and wholesale fares. There are more than 20 major U.S. air courier firms that assign individuals to accompany their international shipments. Among the most dominant is Jupiter Global Ltd, www.jupiterair.com /courier, where you will find applications, requirements, gateways and destinations.

Irene Croft of Kailua, Kona, is a travel writer and 40-year veteran globetrotter. Her column is published in this section every other week.

Irene Croft Jr. of Kailua, Kona, is a travel writer and 40-year veteran globetrotter. Her column is published in this section every other week.