In November, Fallin will face the winner of the Democratic primary race between Attorney General Drew Edmondson and Lt. Gov. Jari Askins.
Fallin flew to Washington before the polls opened Tuesday to cast a vote on a military funding bill and wasn't able to vote Tuesday.
Fallin held off a pesky challenge from conservative state Sen. Randy Brodgon of Owasso. Also in the Republican race were Oklahoma area businessmen Robert Hubbard and Roger Jackson.
A 20-year veteran of Oklahoma politics, Fallin raised more than $2.4 million for the race, more than eight times as much as Brogdon.