Abstract: Disclosed is an improved cryogenic demethanizer, for separating an inlet hydrocarbon gas having a mixture of hydrocarbon components into a residual lighter gas fraction and a heavier liquid fraction. The fractionation column in the demethanizer has a main body portion and an upper portion enlarged with respect to the main body portion. A packing which may be in the form of a plurality of contact trays, or random packing is located in the upper enlarged portion of the column. The invention may be used to retrofit existing cryogenic demethanizers, or used in new installations.