Last weekend Kyle MacDonald in Montreal threw a party to celebrate the fact that he got his new home in exchange for a red paper clip. Starting a year ago, MacDonald bartered the clip for increasingly valuable stuff, including a camp stove and free rent in a Phoenix flat. Having announced his aim (the house) in advance, MacDonald likely got a boost from techies eager to see the Internet pass this daring test of its networking power. "My whole motto (座右铭) was ’Start small, think big, and have fun’, "says MacDonald, 26, "I really kept my effort on the creative side rather than the business side." Yet as odd as the MacDonald exchange was, barter is now big business on the Net. This year more than 400000 companies worldwide will exchange some $10 billion worth of goods and services on a growing number of barter sites. These Web sites allow companies to trade products for a virtual currency, which they can use to buy goods from other members. In Iceland, garment- maker Kapusalan sells a third of its output on the booming Vidskiptanetid exchange, earning virtual money that it uses to buy machinery and pay part of employee salaries. The Troc-Services exchange in France offers more than 4600 services, from math lessons to ironing. This is not a primitive barter system. By creating currencies, the Internet removes a major barrier—what Bob Meyer, publisher of BarterNews, calls "the double coincidence of wants." That is, two parties once not only had to find each other, but also an exchange of goods that both desired. Now, they can price the deal in virtual currency. Barter also helps firms make use of idle capacity. For example, advertising is "hugely bartered" because many media, particularly on the Web, can supply new ad space at little cost. Moreover, Internet ads don’t register in industry-growth statistics, because many exchanges are arranged outside the formal exchanges. Like eBay, most barter sites allow members to "grade" trading partners for honesty, quality and so on. Barter exchanges can allow firms in countries with hyperinflation or nontradable currencies to enter global trades. Next year, a nonprofit exchange called Quick Lift Two (QL2) plans to open in Nairobi, offering barter deals to 38000 Kenyan farmers in remote areas. Two small planes will deliver the goods. QL2 director Gacii Waciuma says the farmers are excited to be "liberated from corrupt middlemen." For them, barter evokes a bright future, not a precapitalist past.

The Internet barter system relies heavily on ______.