NOVELTY - Under partially-loaded operation, a side stream (8) of pure methane product fraction (4) and/or a side stream (9) of residual gas fraction (5) is recycled to a point ahead of cryogenic fractionation (C). Quantities of methane and/or residual gas recycled are sufficiently large, that external sources of refrigeration are obviated.    USE - To produce methane and residual gases, especially from natural gas.    ADVANTAGE - There is no need for an external source of refrigeration, even when working under conditions of partial loading, with this process. Regardless of loading, purity is maintained constant. Capital costs of the plant are reduced. Purification separates CO2, to prevent blockages in lines and valves. The natural gas feedstock comprises in addition: methane (80 vol% or more), nitrogen (10-15 vol %) and higher hydrocarbons. Fractionation is standard, e.g. in two columns; represented by the black box (C). Because of recycling, the process essentially sees full loading at all times, regardless of the feedstock supply rate.    DETAILED DESCRIPTION - Preferred Features: The hydrocarbon rich feedstock (1) to be fractionated, is compressed (V) in single- or multiple stages, before cryogenic fractionation. Recycled pure methane (8) and residual fraction (9) are introduced ahead of the compressor (V); or in the case of multistage compression, they are fed into one or more intermediate stages of compression. The hydrocarbon rich fraction to be fractionated (1, 2) is relieved of components interfering with cryogenic fractionation (C) by purification (P) first. Purification is by adsorption (P) or scrubbing. For regeneration of the purification stage, a side stream of residual gas is supplied, to act as a regeneration gas.    DESCRIPTION OF DRAWING(S) - The drawing shows a block schematic flow diagram of the process.    Cryogenic fractionation (C)    Adsorber or scrubber (P)    Compressor (V)    Hydrocarbon rich feedstock (1)    Methane product fraction (4)    Residual gas fraction (5)    Side stream of pure methane (8)    Side stream of residual gas (9)