Abstract: A gaseous stream (such as a "sour" natural gas stream) composed chiefly of a normally gaseous light hydrocarbon or alkane, such as methane, ethane, propane, or mixtures thereof, containing undesirable constituents, impurities or contaminants, such as carbon dioxide, hydrogen sulfide, water vapor, nitrogen and helium, is mixed with a polar organic liquid, such as methanol, or an aqueous solution of said liquid, such as an aqueous solution of methanol. The resulting mixture is cooled and liquefied and the resulting two-phase liquid mixture (comprising a light phase rich in the desired light hydrocarbon and an impurities-rich heavy phase of said polar organic liquid) is extracted with said polar organic liquid to recover said light hydrocarbon in the liquefied state, e.g. as liquefied, "sweet" natural gas.