A process for the separation of C.sub.2+ hydrocarbons from natural gas under pressure wherein the natural gas is cooled (2, 6), partially condensed, and separated (9) into a liquid fraction and a gaseous fraction. The liquid fraction (10) is subcooled (11) and then expanded into the upper zone of a rectifying column (7). The gaseous fraction (23), after engine expansion (25), is also introduced into the rectifying column (7). During rectification, a product stream (37) containing essentially C.sub.2+ hydrocarbons and a residual gas stream (22) containing predominantly lower-boiling components are obtained. The residual gas stream (22) is initially heated by heat exchange (11) with the liquid fraction (10) and then heated by heat exchange (21) with the gaseous fraction obtained after partial condensation. The residual gas stream is then further heated (6, 2) by heat exchange with the feed stream of natural gas to be partially condensed. The heated residual gas is then engine expanded (28) and reheated again by heat exchange with the feed stream of natural gas to be partially condensed (2).