A woman has won the Nobel prize for economics for the first time since it began in 1968.
Professor Elinor Ostrom, who teaches at Indiana University, won the prize with Professor Oliver Williamson of the University of Berkeley for their separate work in economic governance.
The Nobel Memorial Prize in Economic Sciences is the last of the six Nobel prizes announced this year. Since 1980, it has gone to Americans 24 times.
The economics prize was not among the original Nobel awards, but was created in 1968 by the Swedish central bank in Alfred Nobel's memory.
The Royal Swedish Academy of Sciences cited Professor Ostrom "for her analysis of economic governance," saying her work had demonstrated how common property could be successfully managed by groups using it.
The academy said Professor Williamson developed a theory where business firms served as structures for conflict resolution.
He has argued that hierarchical organisations such as companies represent alternative governance structures, which differ in their approaches to resolving conflicts of interest.
The BBC reports the pair will share the prize of 10 million Swedish kronor ($US1.44 million).
Last year, US Professor Paul Krugman won the prize, in recognition of his analysis of trade patterns and where economic activity takes place.
2009 Nobel Prize winners
Peace: US President Barack Obama
Physics: Charles K Kao, Willard S Boyle and George E Smith
Chemistry: Venatraman Ramakrishan, Thomas A Steitz and Ada E. Yonath
Physiology or Medicine: Elizabeth H Blackburn, Carol W Greider and Jack W. Szostak
Literature: Herta Muller
Economics: Elinor Ostrom and Oliver E Williamson.
