The Mexican oil expropriation (Spanish: expropiación petrolera) (also petroleum expropriation, petroleum nationalization, etc.) was the expropriation of all oil reserves, facilities, and foreign oil companies in Mexico in 1938. It took place when President and General Lázaro Cárdenas declared that all mineral and oil reserves found within Mexico belong to the nation. It is one of the Fiestas Patrias of Mexico, celebrating the date when the President, General Lázaro Cárdenas, declared that all oil reserves found in Mexican soil belonged to the nation, following the principle stated in the Article 27 of the Constitution of 1917. This measure caused an international boycott of Mexican products in the following years, especially by the United States, the United Kingdom and the Netherlands.

The political support of labor unions and the founding of Petromex (before Pemex) immediately after taking power by President Lazaro Cardenas, were the proximate events closest to the Petroleum Expropriation.