Leonid Hurwicz, 90, Nobel Winner

Leonid Hurwicz, who shared the Nobel Prize in economics last year for developing a theory that helps explain how buyers and sellers can maximize their gains, died Tuesday at 90.

Hurwicz, an emeritus economics professor at the University of Minnesota, was given his prize in Minneapolis last December because he couldn't make the trip to Stockholm.

At age 90, he was the oldest person ever to win a Nobel, according to the Royal Swedish Academy of Sciences. He shared his prize with Eric S. Maskin, a professor at the Institute for Advanced Study at Princeton, N.J., and with Roger B. Myerson, 56, a professor at the University of Chicago.

In its announcement, the Royal Swedish Academy of Sciences said the three "laid the foundations of mechanism design theory," which plays a central role in contemporary economics and political science.

Essentially, the three men, starting in 1960 with Hurwicz, studied how game theory can help determine the best, most efficient method for allocating resources, the academy said.

Mr. Myerson, who in 2006 wrote a paper in honor of Hurwicz, said Hurwicz's "concept of incentive compatibility produced in the early 1970s revolutionized economic theory. It was one of the great breakthroughs of social science in the 20th century."