Abstract: A method of and apparatus for separating C.sub.4 hydrocarbons from a feed comprising a gaseous mixture. The feed is cooled and partially condensed in a plurality of successive stages of condensation and phase separation. A gaseous overhead from each separation stage is further cooled and supplied to the next separation stage and the liquid separated from each stage is used to cool the gas. Further refrigeration is supplied to the gas to effect the condensations by indirect heat exchange with a closed cycle refrigerant subjected to a compression/expansion cycle. The feed undergoes no compression and no abrupt expansion during the separation, so that the feed undergoes a pressure decrease due only to friction of the passage of the feed through the apparatus. The pressure loss is no more than about 20 psi. The temperature of the feed is maintained below 150.degree. F. at all times, to prevent polymerization of 1,3-butadiene.