The B18 is a 1.8 L inline four cylinder overhead valve automobile engine produced by Volvo from 1961 through 1968.

The world's highest mileage car,[1] a 1966 Volvo P1800S, traveled more than 4,890,993 km (3,039,122 mi) on its original B18 engine.

[6] On 1 January 2014 the Grainger & Worrall company announced that they had partnered with Axelsson to reproduce the DOHC head for the B18 engine.

[9][10] The 2-litre B20 is a bored-out B18 introduced in 1969, with its bore diameter enlarged to 88.9 mm (3.5 in) and a displacement of 1,986 cc (121.2 cu in).

There are five variations of this engine: The B20E and B20F versions featured larger valves, and intake/exhaust ports and for 1974–1975 switched from electronic D-Jetronic to mechanical K-Jetronic injection.

The 3.0 L (183 cu in) six-cylinder B30 is a B20 with two additional cylinders, introduced for the 1969 model for the newly released Volvo 164.