Over the years, the Southern California proprietor of Cardiff by the Sea Lodge, a 17-room bed-and-breakfast, has used the art of barter to swap hotel rooms that would have otherwise gone vacant for everything from carpet and cleaning services for her business to medical and dental work.

Although bartering has been around since ancient times, the advent of e-commerce tools such as the Internet and an increasingly uncertain economy makes barter an option that is anything but archaic, say barter aficionados.

"It costs me a certain amount to be open whether anyone is in the room or not," said Statser, a member of San Diego's Itex Corp. "So there is always a place in business for barter because it is another source of income.

"Everyone is always looking for the magic key - advertising, discounts - to keep hotel rooms full, but there is never just one solution," said Statser, who has operated the Cardiff lodge since 1991. "It's a lot of different things. And barter is just another key to success."

About 400,000 U.S. companies barter each year, accounting for about $4.3 billion in transactions, according to statistics compiled by the National Association of Trade Exchanges. The World Trade Organization estimates that 15 percent, or $8.4 billion of the $5.62 trillion in international trade, is conducted on a non-cash basis.

Unsurprisingly, barter - the equal exchange of products or services - tends to heat up as the economy slows down, said Tom McDowell, executive director of NATE.

"In an economy like this, businesses still have inventory, still have expenses, but they may not have the customers," said McDowell, whose trade organization represents about 57 North American barter exchanges. "What barter does is bring in new customers and allow businesses to use excess capacity or unsold inventory to pay for things they still need to run their business."

Much of the barter business is confined to barter exchanges such as Itex and International Monetary Systems. The exchanges are essentially membership groups that broker trades within the group and use their own trade credits as "currency."

A barter member - for instance, a hotel or advertising agency - "sells" a commodity such as a vacant room or public relations services to another business member for a set price in barter credits. The barter credits can then be banked and used later to buy a desired product or service that any other exchange member may offer.

Most traditional barter exchanges make money by charging a small monthly membership fee and/or taking a commission on each transaction from the buyer and the seller.

Two of the oldest and most reputable barter exchanges in San Diego are Itex and VIP Barter, though there are a handful of others, including Premier Barter, a Phoenix-based barter exchange that last year purchased Barter of San Diego.

Duncan Banner, owner of the San Diego-based Itex franchise, said barter has always been a useful business tool, but one that is still underutilized.

"When times are good and companies are cranking out money, they don't think about barter, it's a 'if it's not broke, don't fix it' mentality, so they don't think outside the box," said Banner, whose company's 700 barter clients last year traded $8.2 million in goods and services. "If, on the other hand, you find that you are looking out the window a lot and the appointment book isn't full, you need to think about barter."

David Powers, owner of VIP Barter, said barter can be especially attractive for those in the leisure and media industry. His clients barter everything from advertising and media air time to airline seats, hotel rooms, vacation packages and other "perishables."

For some companies, the math can be particularly attractive. For instance, a 200-room San Diego hotel's average occupancy rate might be 80 percent, which leaves about 40 rooms per night vacant and not producing revenue. If the average room rate is $150, that's a loss of $6,000 per day.

Instead of eating the potential loss, hotels can trade rooms for advertising such as radio time or billboards in other cities, supplementing their marketing campaign to bring in other, cash-paying customers, Powers said.

"We convert loss into an avenue that generates more business," Powers said.

Last year, Premier Barter did 9,380 transactions totaling $3.2 million from its 425 members, according to Catherine Cohen, co-owner of the privately held barter exchange.

"Barter is a business strategy to open new markets, win new customers, reduce inventories, drive revenues and increase profitability, all while conserving cash," Cohen said.

In addition to traditional barter exchanges, there are also a growing number of online bartering sites such as SwapThing and BarterBucks, as well as the bartering category at Craigslist.org, the free online classifieds community launched in 1995.

A recent search in San Diego's Craigslist barter section, for example, found some brisk entrepreneurial exchanges, including a professional photographer willing to swap $200 worth of services and photo prints for house cleaning and a contractor willing to install granite kitchen counters for a used truck.

The drawback to Craigslist and other such Internet barter sites is they usually require a perfectly timed double coincidence, Banner said. In the dot-com boom of 2000, several online barter sites emerged, such as BigVine.com, only to fizzle within a few years.

"One thing ... about that kind of bartering is you have to have an exact match - you have to want what the other person has and they want what you have at the same moment in time," Banner said. "At some point it becomes so much work that you'd just rather go out and pay cash."