Models built in the early 1920s included 1,984cc and 3,430cc fours and a six-cylinder 5,598cc model. From 1929 Opel also offered the eight cylinder 5,972cc Regent, built on American lines. Understandably so, because General Motors of Detroit had taken control of Opel in 1928.
New small Opel fours appeared, including the 1,074cc Kadett and 1488cc Olympia: the Kadett became a best-seller. Among six-cylinder Opels were the 2,473cc Super-Six and Kapitan and the 3,626cc Admiral, all with ohv engines.
When World War Two broke out, Opel was the leading European car manufacturer, selling the small versions in large numbers; some 107,000 Kadetts were built from 1937 to 1941. The first Opel car after the war was the pre-war Olympia, now with an ohv 1,488cc four-cylinder engine, which entered production in 1947. The first new 2,473cc six-cylinder Kapitan arrived in 1948. Other models included the Rekord and the 1,200. The year 1962 saw a new, modern Kadett with a 993cc four-cylinder engine. Later, four-cylinder engines up to 1,897cc and six-cylinder power units of Rekord, Commodore and Senator/ Monza 2,586cc were available in the Rekord. Six-cylinder Kapitans and Admirals. had engines up to 2,784cc, while other big Opel cars, including the Diplomat, housed Chevrolet built V8 motors.