Shares in Sweden's Saab jumped almost 30% after it won a $4.5bn (£2.7bn) deal to supply 36 fighter jets to Brazil.
The deal is one of the most valuable ones in emerging markets and Saab had faced competition from rivals Boeing and Dassault Aviation.
Many had expected Boeing or Dassault to emerge as the winner.
The BBC's Gary Duffy in Sao Paulo says Boeing's cause was not helped by a recent row between the US and Brazil over spying allegations.
The US National Security Agency (NSA) has been accused of intercepting emails and messages from President Dilma Rousseff, her aides and state oil company, Petrobras.
David Fleischer, a political scientist at the University of Brasilia, said that Ms Rousseff "had been favouring the Boeing plane and a lot of people thought she would announce her decision during her state visit to Washington".
"Boeing was very close but then the NSA booted them out of the air," he said.
