A vapor fraction containing hydrogen and at least one hydrocarbon selected from the group consisting of C.sub.1 to C.sub.4 hydrocarbons is separated from a hydrogen-rich refinery off-gas feed to give a liquid product fraction. The refinery off-gas is fed to and compressed in a compressor/expander having compressor means and expander means mounted and driven on a common shaft, and then cooled and partially condensed to form a two-phase fluid in a heat exchanger followed by separation of the vapor and liquid product phases of the fluid in a separator or a separator/fractionation column stabilizer unit. The separated vapor phase is transmitted to the compressor/expander unit wherein the vapor is depressurized and partially condensed, thereby driving the compressor. The partially condensed depressurized vapor fraction from the expander and, optionally, the liquid phase product fraction from the separator are transmitted in separate streams to the heat exchanger for separate thermal contact with the compressed feed gas wherein the partially condensed depressurized vapor fraction is fully vaporized and the feed gases are cooled. The fully vaporized fraction and the liquid product fraction are recovered in separate streams.