Leonid Hurwicz, a University of Minnesota professor who shared the 2007 Nobel Prize in economics for developing a theory that helps explain how buyers and sellers can maximize their gains, died Tuesday night.

The 90-year-old Minneapolis resident had been hospitalized for about a week.

Hurwicz was given his prize in Minneapolis in December because he couldn't travel to Stockholm. He was the oldest person to win a Nobel, according to the Royal Swedish Academy of Sciences.

"The first thing I thought was that it was a joke," Hurwicz told the Star Tribune when his prize was announced last October. "Considering that it was 6 in the morning, not a very good joke."

He shared his prize with Eric Maskin, a professor at the Institute for Advanced Study at Princeton, N.J.; and Roger Myerson, a professor at the University of Chicago.

"This was a prize that was long overdue," said Narayana Kocherlakota, chairman of the University of Minnesota economics department.

"He did seminal, foundational work that many people built on. It was great to see it finally acknowledged and recognized," Kocherlakota said in October.

The three Nobel winners studied how game theory can help determine the best, most efficient method for allocating resources.

Hurwicz's ideas have influenced everything from a strategy for reducing acid rain to the allocation of cell phone licenses and the use of tax incentives, Kocherlakota said Wednesday.

When Marcel Richter, a University of Minnesota economics professor, was a newly minted assistant professor, he and several others sat in Hurwicz's lectures.

"He had a reputation as a deep thinker," said Richter, adding that Hurwicz made many contributions outside of the classroom.

He was on the platform committee of the 1968 Democratic Convention in Chicago.

"People trusted him in personal relations," because "it was his consideration of other people's opinions, and his ability to advocate his own positions strongly, and still maintain very good relations," Richter said.

Hurwicz, who never received a graduate degree in economics, studied under or worked with some of the best people in the field.

Hurwicz was born in Moscow of Polish parents who fled World War I. He earned a law degree in 1938 from the University of Warsaw and briefly studied in London.

He came to the United States in 1940. The next year he became a research assistant to Paul Samuelson, an MIT economist and Nobel laureate.

After teaching in Illinois and Iowa, he came to the University of Minnesota in 1951 to teach economics and statistics. After a stint at Stanford, he returned to the university as chairman of the statistics department in 1961. Eight years later, he was named Regents' Professor of Economics.

He retired 20 years ago, but was still doing research, analyzing welfare economics and other topics until recent months. When not working, he enjoyed playing classical music on his piano, said his wife, Evelyn, of Minneapolis.

In addition to his wife of 64 years, he is survived by his daughters, Sarah Kogut of Minneapolis and Ruth Markovitz of Ann Arbor, Mich.; sons, Michael of Eastsound, Wash., and Maxim of Minneapolis.; brother, Henry of Indio, Calif.; seven grandchildren and one great-grandchild.

A memorial service is being planned for the fall at the University of Minnesota.