Continuous gas phase partial oxidn. of an organic cpd. (I) with heterogeneous catalyst in an oxidn. reactor uses a charge gas mixt. contg. (I) O2 and an inert diluent gas (II), which consists partly of combustible gases (IIA). The novelty is that the (IIA) fraction of (II) in the prod. gas stream leaving the oxidn. reactor is not recycled to partial oxidn. but used in another chemical reaction.