辛烷值（英语：Octane Number）是交通工具所使用的燃料抵抗爆震的指标（该指标一般适用于描述汽油的性能），辛烷值越高表示抗震爆的能力越好。

辛烷值一般是区分不同等级汽油的关键标准，比如中国大陆的97号汽油，表示其辛烷值为97，但注意各地区加油站的对汽油的标示方法并不统一，在一些国家其出售的汽油的数值不等于常见的研究法得到的辛烷值（如美国），另一些则根本不以数值标示（如德国）但是马来西亚政府却强逼人民需要Ron95，以赚取更多的收入。

提高汽油辛烷值的方法包括加入四乙基铅及甲基叔丁基醚、碳酸二甲酯、MMT（甲基环戊二烯三羰基锰）等。由于铅是有毒物质，因此许多国家已经不再提供含铅汽油，仅余航空用油仍带有铅。

Octane rating or octane number is a standard measure of the performance of an engine or aviation fuel. The higher the octane number, the more compression the fuel can withstand before detonating (igniting). In broad terms, fuels with a higher octane rating are used in high performance gasoline engines that require higher compression ratios. In contrast, fuels with lower octane numbers (but higher cetane numbers) are ideal for diesel engines, because diesel engines (also referred to as compression-ignition engines) do not compress the fuel, but rather compress only air and then inject fuel into the air which was heated by compression. Gasoline engines rely on ignition of air and fuel compressed together as a mixture, which is ignited at the end of the compression stroke using spark plugs. Therefore, high compressibility of the fuel matters mainly for gasoline engines. Use of gasoline with lower octane numbers may lead to the problem of engine knocking.