Hydrocarbons are recovered from a product purge gas generated in the synthesis of a polyalkene from a feed gas comprising alkene monomer and intermediate hydrocarbons. The purge gas, which is generated by purging the product with an inert gas, comprises inert gas, monomer, by-product heavy hydrocarbons and intermediate hydrocarbons. The recovery method comprises (A): (a) absorbing the heavy hydrocarbons from the purge gas by contact with a scrub liquid feed (31) comprising the intermediate hydrocarbons in an absorption zone (117); (b) withdrawing from the absorption zone a vapour overhead (35) comprising inert gas and alkene monomer and a bottoms scrub liquid (33) comprising heavy hydrocarbons; (c) cooling, condensing and rectifying the overhead in a dephlegmator system (120) to yield a hydrocarbon stream (243) rich in alkene monomer and intermediate hydrocarbons and a warmed light vapour (249) enriched in inert gas; and (d) recycling the absorber bottoms scrub liquid (33) to the polymerisation reactor; or (B): (a') compressing, cooling and partially condensing the purge gas and separating it into a first vapour (30) (containing inert gas, monomer, heavy hydrocarbons and intermediate hydrocarbons) and a hydrocarbon-rich liquid; and (b') recovering the monomer from the vapour by cooling, condensing and rectifying the overhead in a dephlegmator system (120) to yield a hydrocarbon stream (243) and a warmed light vapour (249).    USE -   For recovering hydrocarbons from a purge gas generated in the polymerisation of alkenes such as ethylene and propylene (claimed).    ADVANTAGE -   Both methods remove oligomers and heavier hydrocarbons in a first step and so eliminate the problems caused by the freeze-out of these hydrocarbons when low temperature condensation is used for the recovery of light and intermediate hydrocarbons. The hydrocarbon-based scrub liquid eliminates the problems of adsorbent deactivation or permanent adsorption which can occur in adsorption-based methods. Because the scrub liquid is compatible with the polymerisation reactor operation, the absorption step can be operated on a once-through basis, and a separate step for recovery of the monomer from the absorption liquid is not required.