Process for producing a synthesis gas product stream having an adjustable hydrogen-carbon monoxide ratio (H 2 /CO ratio) and a pure hydrogen stream from an input stream containing hydrocarbons, comprising the steps of: (a) providing the input stream containing hydrocarbons, (b) supplying the input stream containing hydrocarbons to a synthesis gas production plant comprising a steam reforming stage or an autothermal reforming stage or a partial oxidation stage or a combination of at least two of the stages to, (c) at least partial conversion of the input stream containing hydrocarbons in the synthesis gas production plant under synthesis gas production conditions to afford a raw synthesis gas stream containing hydrogen (H 2) and carbon monoxide, (d) discharging a raw synthesis gas stream from the synthesis gas production plant, (e) introducing at least a proportion 1 of the raw synthesis gas stream into a CO conversion plant comprising at least one CO conversion stage, converting the proportion of the raw synthesis gas stream introduced into the CO conversion plant under CO conversion conditions to afford a converted synthesis gas stream, discharging the converted synthesis gas stream, (f) introducing the raw synthesis gas stream and/or the converted synthesis gas stream into a sorption apparatus for removal of acidic gas constituents, especially carbon dioxide and hydrogen sulfide, using a physical or chemical sorption process, discharging a deacidified synthesis gas stream from the sorption apparatus, (g) introducing at least a proportion 2 of the deacidified synthesis gas stream into a first hydrogen enrichment stage containing a hydrogen selective membrane as the separating means, separating the deacidified synthesis gas stream into a hydrogen-enriched permeate stream and into a hydrogen-depleted retentate stream, (h) introducing the hydrogen-enriched permeate stream and the proportion of the deacidified synthesis gas stream not passed to the first hydrogen enrichment stage into a second hydrogen enrichment stage operating according to the principle of pressure swing adsorption, (i) discharging a pure hydrogen stream and a carbon monoxide-containing residual gas stream from the second hydrogen enrichment stage, (j) discharging the hydrogen-depleted retentate stream from the first hydrogen enrichment stage as a synthesis gas product stream, (k) wherein the proportion 1 and/or the proportion 2 are chosen such that the molar H 2 /CO ratio required for the synthesis gas product stream is obtained. (a) providing the input stream containing hydrocarbons, (b) supplying the input stream containing hydrocarbons to a synthesis gas production plant comprising a steam reforming stage or an autothermal reforming stage or a partial oxidation stage or a combination of at least two of the stages to, a steam reforming stage or an autothermal reforming stage or a partial oxidation stage or a combination of at least two of the stages to, (c) at least partial conversion of the input stream containing hydrocarbons in the synthesis gas production plant under synthesis gas production conditions to afford a raw synthesis gas stream containing hydrogen (H 2) and carbon monoxide, (d) discharging a raw synthesis gas stream from the synthesis gas production plant, (e) introducing at least a proportion 1 of the raw synthesis gas stream into a CO conversion plant comprising at least one CO conversion stage, converting the proportion of the raw synthesis gas stream introduced into the CO conversion plant under CO conversion conditions to afford a converted synthesis gas stream, discharging the converted synthesis gas stream, (f) introducing the raw synthesis gas stream and/or the converted synthesis gas stream into a sorption apparatus for removal of acidic gas constituents, especially carbon dioxide and hydrogen sulfide, using a physical or chemical sorption process, discharging a deacidified synthesis gas stream from the sorption apparatus, (g) introducing at least a proportion 2 of the deacidified synthesis gas stream into a first hydrogen enrichment stage containing a hydrogen selective membrane as the separating means, separating the deacidified synthesis gas stream into a hydrogen-enriched permeate stream and into a hydrogen-depleted retentate stream, (h) introducing the hydrogen-enriched permeate stream and the proportion of the deacidified synthesis gas stream not passed to the first hydrogen enrichment stage into a second hydrogen enrichment stage operating according to the principle of pressure swing adsorption, (i) discharging a pure hydrogen stream and a carbon monoxide-containing residual gas stream from the second hydrogen enrichment stage, (j) discharging the hydrogen-depleted retentate stream from the first hydrogen enrichment stage as a synthesis gas product stream, (k) wherein the proportion 1 and/or the proportion 2 are chosen such that the molar H 2 /CO ratio required for the synthesis gas product stream is obtained.