TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Process: The feed gas in step (a) has been desulfurized before mixing the feed gas and the recycled methane-rich gas. The step (a) further comprises shifting the gas mixture with water and/or steam in a water-gas shift reaction before reacting carbon monoxide and hydrogen in step (b). The water-gas shift reaction and the reaction of carbon monoxide and hydrogen are carried out in one reactor vessel. The step (c) comprises cooling the methane-rich product gas produced in step (b) to produce a cooled methane-rich product gas; removing water from the cooled methane-rich product gas to produce a dried and cooled methane-rich product gas; and treating the dried and cooled methane-rich product gas to remove carbon dioxide to produce the methane-rich carbon dioxide-lean gas. The molar ratio of recycled methane-rich gas to feed gas in the gas mixture of step (a) is equal to or less than 2:1. In the process: 1-99 vol.% of the methane-rich product gas produced in step (b) is treated to remove carbon dioxide to produce a methane-rich carbon dioxide-lean gas and essentially all of the methane-rich carbon dioxide-lean gas is recycled to mixing step (a) as recycled methane-rich gas; and at least part of the methane-rich product gas produced in step (b) and/or at least part of the methane-rich carbon dioxide-lean gas produced in step (c) is forwarded to a subsequent adiabatic methanation reactor to produce a further methane-rich product gas. The process further comprises the use of the methane-rich product gas as a substitute for natural gas. The feed gas in step (a) is synthesis gas obtained by reacting a carbonaceous feed and an oxidant in a gasification reaction. The step (a) comprises reacting a carbonaceous feed and an oxidant in a gasification process to produce a synthesis gas comprising carbon monoxide and hydrogen, where the synthesis gas is desulfurized to produce a desulfurized synthesis gas, where at least part of the desulfurized synthesis gas is reacted with water and/or steam in a water-gas shift reaction to produce a shifted synthesis gas, and the shifted synthesis gas is mixed with a recycled methane-rich gas, comprising methane, to produce a gas mixture, which gas mixture comprises carbon monoxide, hydrogen and methane. Preferred Components: The recycled methane-rich gas comprises less than 10 vol.% of water, less than 10 vol.% of carbon dioxide and more than 25 vol.% of methane. The carbonaceous feed is coal or petroleum coke. EXAMPLE - Gas mixture stream (comprising water (32.7 mol.%), nitrogen (0.2 mol.%), argon (0.1 mol.%), hydrogen (34.8 mol.%), carbon monoxide (5.9 mol.%), methane (3.6 mol.%) and carbon dioxide (22.7 mol.%)) was converted over a fixed bed of water-gas shift catalyst and a fixed bed of methanation catalyst in a first methanation reactor into a stream of methane-rich product gas (comprising water (49.1 mol.%), nitrogen (0.3 mol.%), argon (0.1 mol.%), hydrogen (13.4 mol.%), carbon monoxide (2.8 mol.%), methane (11.9 mol.%) and carbon dioxide (22.5 mol.%)). The stream was cooled and split into a first split methane-rich gas stream and a second split methane-rich gas stream. The first split methane-rich gas stream was recycled as stream (comprising nitrogen (0.9 mol.%), argon (0.2 mol.%), hydrogen (43.7 mol.%), carbon monoxide (9 mol.%), methane (38.8 mol.%), and carbon dioxide (7.4 mol.%)), after cooling, water and carbon dioxide were removed. The second split methane-rich gas stream (comprising water (49.1 mol.%), nitrogen (0.3 mol.%), argon (0.1 mol.%), hydrogen (13.4 mol.%), carbon monoxide (2.8 mol.%), methane (11.9 mol.%) and carbon dioxide (22.5 mol.%)) were forwarded to a second methanation reactor and converted into a second stream of methane-rich product gas (comprising water (56.9 mol.%), nitrogen (0.3 mol.%), argon (0.1 mol.%), hydrogen (3 mol.%), carbon monoxide (0.2 mol.%), methane (16.3 mol.%) and carbon dioxide (22.4 mol.%)). The second stream of methane-rich product gas was cooled at 300 degrees C, then forwarded to a third methanation reactor and converted into a third stream of methane-rich product gas (comprising water (58.8 mol.%), nitrogen (0.3 mol.%), argon (0.1 mol.%), hydrogen (0.5 mol.%), methane (17.2 mol.%), and carbon dioxide (23.2 mol.%)). The product stream of the first methanation reactor was split up in a ratio of gas to be recycled and gas to be forwarded to the second methanation reactor of 9:16.5.