在化学和石油地质学中，裂化反应（Cracking，或称裂解作用、裂炼反应）是将复杂有机分子（如干酪根或重质烃）通过打开碳-碳键断裂成简单分子（如轻质烃）的过程。裂化的速率和最终产物十分依赖于温度和所使用的催化剂。裂化可将大的烷烃断裂成更小的、更有用的烷烃和烯烃。简而言之，烃的裂化就是将长链的烃断裂成短链的烃的过程。

更广义的说，在石油化学外的其他领域中，“裂化（裂解）”这个术语用于描述任何在热、催化剂或溶剂的作用下的分子断裂，如分解蒸馏或热裂解过程。

流化催化裂化产生大量的汽油和液化石油气（LPG）, 而加氢裂化是喷气燃料、柴油、石脑油的主要来源，同时也产生LPG。

In petroleum geology and chemistry, cracking is the process whereby complex organic molecules such as kerogens or long chain hydrocarbons are broken down into simpler molecules such as light hydrocarbons, by the breaking of carbon-carbon bonds in the precursors. The rate of cracking and the end products are strongly dependent on the temperature and presence of catalysts. Cracking is the breakdown of a large alkane into smaller, more useful alkanes and alkenes. Simply put, hydrocarbon cracking is the process of breaking a long-chain of hydrocarbons into short ones. This process might require high temperatures and high pressure.