NOVELTY - An expanded gas stream (34a) is supplied between absorbing unit and mass transfer unit. Distillation vapor streams (s1,s2) are collected from upper/lower regions of absorbing unit and cooled in heat and mass transfer units (hm1,hm2) to condense less volatile components and to strip more volatile components. A control unit is adapted to maintain temperature of distillation vapor stream (s2) at temperature, whereby major portion of components and heavier hydrocarbon components are recovered in relatively less volatile fraction, in order to separate gas stream.    USE - Separation of gas used for recovery of butane and pentane.    ADVANTAGE - The method is environmentally-friendly, and enables efficient recovery of butane and pentane, with reduced energy consumption. The compact arrangement of processing assembly in the apparatus replaces 5 separate equipment e.g. fractionation tower, reboiler, reflux condenser, reflux separator and reflux pump with 1 equipment e.g. processing assembly, in order to eliminate interconnecting piping, and reduce capital cost of processing plant, capital cost of platform or shin on which it is installed and number of potential leak sources in the plant.    DETAILED DESCRIPTION - A gas stream (31) comprises methane, 2-5C components, and heavier hydrocarbon components. The gas stream is expanded to lower pressure. The expanded gas stream is supplied as feed between absorbing unit and mass transfer unit housed in processing assembly. The absorbing unit is located above mass transfer unit. A distillation vapor stream (s1) is collected from upper region of absorbing unit and cooled in heat and mass transfer unit (hm1) housed in processing assembly to condense less volatile components from distillation vapor stream (s1), to form condensed stream and distillation vapor stream (s2). The distillation vapor stream (s2) is discharged from processing assembly as volatile residue gas fraction. The condensed stream is supplied as top feed to absorbing unit. A distillation liquid stream (35) is collected from lower region of mass transfer unit and heated in heat and mass transfer unit (hm2) housed in processing assembly to strip the more volatile components from distillation liquid stream. The heated and stripped distillation liquid stream is discharged from processing assembly as relatively less volatile fraction. A control unit is adapted to maintain temperature of distillation vapor stream (s2) at temperature, whereby major portion of components and heavier hydrocarbon components are recovered in relatively less volatile fraction, in order to separate gas stream. An INDEPENDENT CLAIM is included for apparatus for separation of gas stream, which consists of expansion unit connected to receive gas stream in pressure and expand it to lower pressure, processing assembly connected to expansion unit to receive expanded gas stream as feed between absorbing unit and mass transfer unit housed in processing assembly, vapor collecting unit housed in processing assembly and connected to absorbing unit to receive distillation vapor stream (s1), heat and mass transfer unit (hm1) connected to vapor collecting unit to receive distillation vapor stream (s1), absorbing unit further connected to heat and mass transfer unit (hm1) to receive condensed stream as top feed, liquid collecting unit connected to mass transfer unit to receive distillation liquid stream, heat and mass transfer unit (hm2) connected to liquid collecting unit to receive distillation liquid stream and heat it, and control unit adapted to maintain temperature of distillation vapor stream (s2).    DESCRIPTION OF DRAWING(S) - The drawing shows a flowchart of gas separation.    Gas stream (31)    Cooled feed stream (31a)    Vapor stream (34)    Expanded gas stream (34a)    Liquid stream (35)