WHEN Steven P. Jobs, Apple’s chief executive, appeared in public recently for the first time in months, he revealed that he had received a liver transplant from the victim of a car crash. “I wouldn’t be here without such generosity,” Mr. Jobs said, adding that he hoped that many people would become organ donors.

With the help of a little behavioral economics, it is possible to make that hope a reality.

More than 20,000 organ transplants take place every year in the United States, with a vast majority coming from deceased donors. Demand greatly exceeds supply: in 2006, for example, 3,916 patients died while waiting for kidneys, according to the National Kidney Foundation.

Some economists have come up with a simple solution: a market allowing the buying and selling of organs. Because people have two kidneys and need only one to live, a robust market could greatly increase supply.

The idea may have some merit, but it is spectacularly unpopular. As the Harvard economist Alvin Roth has noted, many people consider it “repugnant,” mainly for two reasons. First, they object to the possibility of rich people buying their way to the front of the line. (The hospital where Mr. Jobs’s procedure took place said he received the liver transplant because he was the sickest person on its waiting list who matched the donor’s blood type.) Second, they object to incentives that would induce the poor to sell their kidneys.