NOVELTY - Converting methane into higher alkane mixture comprising greater than or equal to 3C alkanes involves: contacting methane with metal catalyst (C1) that initiates splitting and recombining of carbon-carbon and/or carbon-hydrogen and/or carbon-metal bonds, so as to form mixture (M1) of ethane/hydrogen; fractionating mixture to separate and isolate ethane; and contacting mixture obtained in step (1)/ethane isolated in step (2) with metal catalyst (C2) capable of producing higher alkanes by self/cross metathesis, to form a mixture of methane and the higher alkanes.    USE - For converting methane into a higher alkane mixture comprising greater than or equal to 3C alkanes (preferably greater than or equal to 4C, especially greater than or equal to 5C alkanes) (claimed) useful as fuels and as chemicals in refineries.    ADVANTAGE - The method provides a low cost conversion of methane into mixtures of higher alkanes, which are in liquid form under standard temperature and pressure conditions and hence can be easily transported in liquid form. The method is simple and realizable at relatively low costs enabling it to be installed directly on the natural gas deposit sites. The method is relatively inexpensive, requires lower capital and operating costs in comparison with known processes, as the reaction takes place at moderate temperatures and pressures. The method requires very small amounts of cryogenic supplying and does not require the need of oxygen. The method allows production of higher alkane mixture (preferably liquid alkane mixture) with a high degree of purity and completely free of alkenes, alkynes, aromatic compounds, carbon monoxide, carbon dioxide, sulfur- or nitrogen-containing products. The method does not produce waste products and hence can be considered as clean process for the environment. The method allows production of higher alkane mixture (preferably liquid mixture of alkanes having narrow distribution of number of carbons) that can be easily processed into high value fuels and chemicals in refineries. The higher alkane mixture prepared by the method exhibits a very high ''carbon atom efficiency'' which is higher than 95 (preferably higher than 99)%. The method produces greater amount of hydrogen that can be isolated and used for supplying sufficient thermal and/or electrical energies for running the process.    DETAILED DESCRIPTION - Converting methane into a higher alkane mixture comprising greater than or equal to 3C alkanes involves: a stage 1) including contacting methane with a metal catalyst (C1) capable of producing, in contact with alkane, reactions including the splitting and recombining of carbon-carbon and/or carbon-hydrogen and/or carbon-metal bonds, so as to form by a non-oxidative methane coupling reaction, a mixture (M1) comprising ethane and hydrogen; a stage 2) including fractionating the mixture (M1), so as to separate and to isolate the ethane; and a stage 3) including contacting the mixture (M1) obtained in stage (1) or preferably the ethane isolated in stage (2) with a metal catalyst (C2) capable of producing, in contact with alkane, reactions including the splitting and recombining of carbon-carbon and/or carbon-hydrogen and/or carbon-metal bonds, where the catalyst is identical to or different from the catalyst (C1), so as to form by simultaneous ethane self- and cross-metathesis reactions, a mixture (M2) comprising methane and the higher alkane mixture comprising the greater than or equal to 3C alkanes and fractionating the mixture (M2) so as to separate and to isolate the higher alkane mixture.