The gasoline-powered Oldsmobile Model R, also known as the Curved Dash Oldsmobile, is credited as being the first mass-produced automobile, meaning that it was built on an assembly line using interchangeable parts. It was introduced by the Oldsmobile company in 1901 and produced through 1903; 425 were produced the first year, 2,500 in 1902, and over 19,000 were built in all. When General Motors assumed operations from Ransom E. Olds on November 12, 1908, GM introduced the Oldsmobile Model 20, which was the 1908 Buick Model 10 with a stretched wheelbase and minor exterior changes. It was a runabout model, could seat two passengers, and sold for US$650 ($ in dollars). While competitive, due to high volume, and priced below the US$850 two-seat Ford Model C "Doctor's Car", it was more expensive than the Western 1905 Gale Model A roadster at US$500. The Black sold for $375, and the Success for US$250. It was built as a city car for short distance driving, while the larger Model S could carry four passengers and could travel longer distances. The flat-mounted, water-cooled, single-cylinder engine, situated at the center of the car, produced , relying on a brass gravity feed carburetor. The transmission was a semiautomatic design with two forward speeds and one reverse. The low-speed forward and reverse gear system is a planetary type (epicyclic). The car weighed and used Concord springs. It had a top speed of . The car's success was partially by accident; in 1901, a fire destroyed a number of other prototypes before they could be approved for production, leaving the Curved Dash as the only one intact. As workers were attempting to move the prototypes out of the burning building, they were only successful at rescuing one prototype, the Model R Curved Dash. In 1904, the Model R was replaced by the Model 6C, which had a larger 1,931 cc engine, drum brakes replaced the band brake. After 2,234 copies, the 6C model was discontinued in December 1904. In 1905, the Model B was introduced with more improvements. The engine received improved cooling and a new flywheel, and the handbrake now worked on the differential instead of the gearbox. The leaf spring suspension was modified so that the reinforced axles were connected to all spring elements. In 1906, the car received celluloid side window curtains. The dashboard was also offered with an upright position, called the Straight