The Bentley S1 was a luxury car produced by Bentley Motors Limited from 1955 through 1959. It marked Bentley’s parent, Rolls-Royce, reducing the differences between their Bentley and Rolls-Royce models, with the S1 differing only in its radiator design and badging from the Rolls-Royce Silver Cloud I.

The models shared the 4.9 L (4887 cc/298 in³) straight-6 engine, with this being the last vehicle to use descendants of the engine originally used in the Rolls-Royce Twenty from 1922 to 1929. The bore was 95.25 mm (3.7 in), stroke was 114.3 mm (4.5 in) and compression ratio 6.6:1. Twin SU carburetors were fitted, with upgraded models from 1957. A 4-speed automatic transmission was standard, with a 4-speed manual available as an option until 1957. Two wheelbases were produced: 123 in (3124 mm) and, from 1957, 127 in (3226 mm).