During the war all car plants are forced to built certain vehicles, in case of Opel these are trucks. After the war success cheerfully goes until the worldwide economy crisis strikes. At the beginning of the 1920s market shares grow to more than one third. With the model "Laubfrosch" (tree frog) mass production is introduced to Germany. In 1928 a speed of 238 km/h is reached with a rocket propulsion for the first time.

In the crisis years 1929/30 the company is sold to General Motors, however, remains independant in many decisions. In 1931 the Opel Blitz (flash) develops. Demand for this truck increases in such a way that in 1935 a new production plant is built in Brandenburg. In the same year famous Opel Olympia comes out in time for the Berlin Olpympic Games 1936. With its self-supporting all-steel body this car replaces the predecessors with their U-profile frames and wooden bodies. The alternative, the Opel P4, is quite interesting as well which offeres the old technology, however, for a sensationally favorable price. In 1936 an Opel with the name 'Kadett ' is implemented for the first time. After selling bicycle production to NSU, Opel concentrates on vehicles, surpasses the until then leading french manufacturers and becomes most significant producer in Europe. Supported by General Motors, Opel enters the world market. In 1937 they reach the upper class with the Admiral. 05/12