A process for the separation of carbon dioxide and, optionally, other acid gas components in a distillation column, operated at high pressure and low temperature, from a gaseous mixture comprising one or more hydrocarbons, including particularly methane, and hydrogen. In its preferred aspects, the feed is predominantly methane, suitably from about 30 to about 85 mole percent and preferably from about 50 to about 80 mole percent methane. The concentration of hydrogen in the gaseous mixture will be sufficient to provide from about 6 to about 34 mole percent, preferably from about 15 to about 25 mole percent hydrogen in the rectification portion of the distillation column. The separation can be effected in a single column usually having from about 20 to about 30 theoretical distillation stages and the feed can be one constituted ab initio within the desired ranges of composition, or modified by addition of components just prior to or at the time of distillation.