Process for the production of an olefin comprising partially combusting in a reaction zone a mixture of a hydrocarbon and an oxygen-containing gas in the presence of a catalyst which is capable of supporting combustion beyond the fuel rich limit of flammability to produce the olefin. The superficial feed velocity of the mixture is at least 250 cm s.sup.-1 at standard temperature and operating pressure, with the proviso that where the catalyst is an unsupported catalyst, the superficial feed velocity of the mixture is at least 300 cm s.sup.-1 at standard temperature and operating pressure. The process is carried out at a pressure of at least 1.3 bara and the reaction zone is not externally heated.