A process for treating an effluent gas stream arising from a manufacturing operation that produces an olefin or an olefin derivative to recover unreacted olefin. The process involves compressing the effluent gas stream, which comprises an olefin, a paraffin, and a third gas, to produce a first compressed stream, then directing the first compressed stream to a membrane separation pretreatment step. The permeate stream withdrawn from this step is enriched in olefin and is sent to a second compressor, which produces a second compressed stream that is then cooled and condensed. The condensation step produces a liquid condensate and an uncondensed gas stream. The uncondensed gas stream undergoes a second membrane separation step to produce another olefin-enriched permeate stream, which is recirculated within the process prior to the second compression step, and an olefin-depleted residue stream, which may be purged from the process.