The Oldsmobile 98 (spelled Ninety-Eight from 1952 to 1991, and Ninety Eight from 1992 to 1996) is the full-size flagship model of Oldsmobile that was produced from 1940 until 1942, and then from 1946 to 1996. The name – reflecting a “Series 90” fitted with an 8-cylinder engine – first appeared in 1941 and was used again after American consumer automobile production resumed post-World War II. It was, as it would remain, the division’s top-of-the-line model, with lesser Oldsmobile’s having lower numbers such as the A-body 66 and 68, and the B-body 76 and 78. The Series 60 was retired in 1949, the same year the Oldsmobile 78 was replaced by the 88. The Oldsmobile 76 was retired after 1950. This left the two remaining number-names to carry on into the 1900s as the bread and butter of the full-size Oldsmobile lineup until the Eighty Eight-based Regency replaced the 98 in 1997.

Occasionally additional nomencaiture was used with the name, such as L/S and Holiday, and the 98 Regency badge would become increasingly common in the later years of the model. The 98 shared its General Motors C-body platform with Buick and Cadillac.

Since it was the top-line Oldsmobile, the series had the mist technologically advanced items available, such as the Hydramatic automatic transmission, the Autronic Eye, an automatic headlight dimmer, and Twilight Sentinel (a feature that automatically turned the headlights on and off via a light sensor and a delay timer, as controlled by the driver), and the highest-grade interior and exterior trim.