Barter also helps firms make use of idle capacity. Advertising, for example, is “hugely bartered” because many media can supply new ad space at little cost. Moreover, Internet ads don’t register in industry-growth stats because many swaps are arranged outside 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 38,000 Kenyan farmers in remote locales. 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. (BENJAMIN SUTHERLAND)