A method of processing synthesis gas improves the quality of the synthesis gas by using a water gas shift reaction to increase the molar ratio of hydrogen to carbon monoxide (H2:CO) in an efficient manner. A first steam of hot natural gas-based synthesis gas having a first higher molar ratio of H2:CO is combined with a second stream of quenched synthesis gas having a second lower molar ratio of H2:CO to provide a blend of synthesis gas having a third molar ratio of H2:CO that is between the first and second molar ratios. A non-catalytic water gas shift reaction increases the molar ratio of H2:CO to a fourth molar ratio that is higher than the third molar ratio, and can be about equal to or greater than the first molar ratio without supplying external heat.