Distillative separations of hydrocarbon feed mixtures containing at least methane and carbon dioxide, as well as other components, such as ethane, higher hydrocarbons, and hydrogen sulfide are disclosed. In the separations described, methane is preferably separated from an acid gas under conditions of composition, temperature and pressure which would normally produce acid gas solids. Acid gas solids are prevented by adding a liquid solids-preventing agent into this distillation column. A second distillation column is subsequently employed to further separate the feed gas mixture. The second distillation column is operated under conditions which an azeotrope would normally form between the light hydrocarbon and carbon dioxide, which azeotrope would limit the carbon dioxide overhead composition. The azeotrope is prevented by introducing an agent for preventing azeotrope formation. Alternatively, the second distillation column may be operated to separate carbon dioxide from hydrogen sulfide. In this case, a liquid agent is added to the second distillation column to increase the relative volatility of carbon dioxide to hydrogen sulfide. All liquid agents preferably comprise a C.sub.3 -C.sub.6 alkane, such as butane, or a mixture of such alkanes.