汽油引擎（Gasoline Engine或Petrol Engine）是使用汽油作为燃料的内燃机。

1883年德国人G.戴姆勒成功制造汽油机。二战前，汽油机用作1千瓦以下的农业、园艺机具的动力，大到数千瓦的航空发动机。二战后，汽油机的用途有所缩小，仍用于小功率内燃机、摩托车、轿车、小型飞机和轻型货车等。分为化油器式和汽油喷射式；至1980年代，汽油喷射式的应用增多。

汽油机一般采用往复活塞式结构，由本体（缸盖、缸体、曲轴箱）、曲柄连杆机构、配气系统、供油系统、润滑系统和点火系统等组成。

A petrol engine (known as a gasoline engine in American English) is an internal combustion engine with spark-ignition, designed to run on petrol (gasoline) and similar volatile fuels. The first practical petrol engine was built in 1876 in Germany by Nikolaus August Otto, although there had been earlier attempts by Étienne Lenoir, Siegfried Marcus, Julius Hock and George Brayton. The first petrol combustion engine (one cylinder, 121.6 cm displacement) was prototyped in 1882 in Italy by Enrico Bernardi. In most petrol engines, the fuel and air are usually pre-mixed before compression (although some modern petrol engines now use cylinder-direct petrol injection). The pre-mixing was formerly done in a carburetor, but now it is done by electronically controlled fuel injection, except in small engines where the cost/complication of electronics does not justify the added engine efficiency. The process differs from a diesel engine in the method of mixing the fuel and air, and in using spark plugs to initiate the combustion process. In a diesel engine, only air is compressed (and therefore heated), and the fuel is injected into very hot air at the end of the compression stroke, and self-ignites.