 Ōi, as commander of the Japanese Trans-Baikal Expeditionary Force, signed a treaty with the Far Eastern Republic in May 1920, which set the stage for the withdrawal of Japanese forces from Siberia.He returned to Japan in July 1920 and a seat on the Supreme War Council.In November 1920, he was awarded with the Grand Cordon of the Order of the Golden Kite and the Grand Cordon of the Order of the Rising Sun.