NOVELTY - Methane-rich gas is produced by feeding biomass and/or fossil fuels to a first reactor to form gaseous reaction products, where the first reactor has a hydrogasification reactor which is fed with hydrogen coming from an external source. The product gas has a Wobbe-index of 40-45, preferably 42-45 MJ/m3 (s.t.p.), and a methane molar% of at least 75, preferably 80%.    USE - For producing methane-rich product gas (SNG).    ADVANTAGE - The invention provides a process, in which a hydrogen can be stored efficiently and economically in chemically bound form with relatively little carbon monoxide being present in the synthesis gas formed, and a simple and a relatively small methanation reactor used in the process. The use of the high-temperature plasma process to produce hydrogen from natural gas in combination with the hydrogasification process has the advantage that the Carbon Black and Hydrogen (CBandH) process yields pure carbon. The reduction in calorific value as a result of the conversion of natural gas into hydrogen being compensated for by more than 100%, by back-reaction of the hydrogen to form SNG. This ensures that the fossil carbon disappears from the chain, where sustainable carbon is fed from the biomass with a net gain in energy, owing to the introduction of biomass to an amount roughly 60%.    DETAILED DESCRIPTION - Methane-rich gas (SNG, Synthetic Natural Gas) is produced by feeding biomass and/or fossil fuels to a first reactor to form gaseous reaction products and feeding the reaction products from the first reactor to a methanation reactor in which the gaseous reaction product fed are converted into the methane-rich product gas. The first reactor comprises a hydrogasification reactor which is fed with hydrogen. The hydrogen coming from an external source and in that the product gas (SNG) has a Wobbe-index of 40-45, preferably 42-45 MJ/m3 (s.t.p.), and having a methane molar percentage of at least 75, preferably 80%.    DESCRIPTION OF DRAWING(S) - The drawing shows the process stream for forming substitute natural gas (SNG).    feeder (1)    dryer (2)    hydrogasification apparatus (3)    injection line (4')    feed line (4, 5)    outlet (6)    heat exchanger (9, 11, 14, 18)    gas purification (7)    discharge line (8, 16)    methanation reactor (12)    water separator (15)    steam generator (19)    steam turbine (20)