After the end of the war, Oeser was once again a member of the Prussian diet, first of the Landesversammlung, the constituent assembly of Prussia in 1919-21 and then 1921-24 of the Landtag, this time for the
German Democratic Party (DDP). After March 1919, he was also Minister for Public Works in the Prussian government, making him responsible for infrastructure including the railways. During the
Kapp-Lüttwitz Putsch of March 1920, Oeser was one of those arrested by the putschists. To prevent a strike by railway workers, Kapp wanted to release Oeser, who insisted that the other Prussian ministers should also be released. The next day, Oeser and Prussian Minister of Finance demanded Kapp's resignation and threatened him with a strike by railway workers. Nevertheless, after the end of the putsch the railway workers' union asked for Oeser's dismissal, claiming he had failed to oppose the putsch vigorously enough. Oeser remained in office and was in charge of transferring control over the railways to the Reich. He then left the Prussian government in April 1921 and became
Landeshauptmann (provincial head) of the
Province of Saxony. In the cabinet of
Wilhelm Cuno, Oeser became
Reichsminister des Innern (interior minister) in November 1922. As a staunch democrat and republican, Oeser was a firm supporter of the
Weimar Constitution. During the
Occupation of the Ruhr, Oeser hoped for France to incur material losses through a devaluation of the franc. He supported the policy of passive resistance, despite the damaging effect it had on the German economy, thinking it might be used not just to end the
Ruhrkampf but also to achieve a revision of the much-despised
Treaty of Versailles. After the Cuno cabinet resigned in August 1923, Oeser took over the
Reich Transport Ministry () in the cabinet of
Gustav Stresemann. In the coalition crisis of November 1923 he favoured an exit by the Social Democrats from the cabinet but overestimated their willingness to tolerate a minority government. In the subsequent cabinet of
Wilhelm Marx Oeser prepared the
Reichsbahn for its independence as a formally private institution. In early April 1924,
Reichspräsident Friedrich Ebert named Oeser as temporary general director of the Reichsbahn, supported by a provisonary board of directors made up of the ministries secretaries of state. To serve its intended role under the
Dawes plan, the Reichsbahn required a supervisory board among whose members were some foreigners. Oeser defended this constellation in the Reichstag against attacks from the
NSDAP and
DNVP. At the end of September, the supervisory board of the Reichsbahn designated Oeser as general director. He left the cabinet formally on 11 October and concentrated on reforming the Reichsbahn. In 1925, he became seriously ill and died on 3 June 1926 in Berlin. Oeser had been married to Emilie Oeser. ==Works==