The preparation and characterisation of adsorption-selective microporous carbon membranes is described. The prepared membranes can separate the components of a gas mixture depending on their adsorption properties instead of the molecular size. Thus, these membranes are suitable to separate non-adsorbable or weakly adsorbable components (i.e. N-2, H-2, O-2, etc.) from the more strongly adsorbable components (i.e. hydrocarbons) in a gas mixture. The membrane is prepared from deposition of a thin film of a phenolic resin on the inner face of an alumina tube. After carbonisation (under vacuum at 700 degrees C) and air oxidation (300-400 degrees C), a carbon membrane with the described characteristics is obtained. The prepared membrane shows high permeabilities and selectivities towards separation of gas mixtures formed by hydrocarbons and N-2. As an example, the values of permeability and selectivity (hydrocarbon/N-2) for the separation of a complex gas mixture formed by 16.3% CH4, 16.1% C2H6, 16.2% C3H8, 20% C3H6 and 31.4% N-2 are: CH4, 320 Barrer (alpha=2.6); C2H6, 1104 Barrer (alpha=9.1); C3H6. 2930 Barrer (alpha=23.4); C3H8, 2850 Barrer (alpha=22.8).