This chapter present an overview of the applications of gas/vapor permeation in the three main fields of the hydrocarbon-processing industry, viz:natural or biogas treatmentpetroleum refining (which aims at producing fuels)production of petrochemicals (which aims at producing first intermediates, i.e. olefins and aromatics, for raw chemicals or polymers production).The review will:present the technical challenges and markets the permeation membranes are meant to addressgive a detailed presentation of existing commercial membrane technologies (providers, membrane materials, available technical and economic performances) illustrated, when possible, with case studiesprovide the future trends for research in each addressed application.