NOVELTY - A continuous process for anaerobic bioconversion of gas substrate comprising carbon monoxide, hydrogen and carbon dioxide in aqueous menstruum containing microorganisms suitable for converting substrate to alcohol, involves continuously contacting gas substrate with aqueous menstruum to bioconvert gas substrate to alcohol and providing alcohol-containing menstruum and depleted gas phase; continuously withdrawing depleted gas phase from aqueous menstruum; continuously or intermittently withdrawing portion of menstruum for recovery of alcohol.    USE - For anaerobic bioconversion of gas substrate comprising carbon monoxide, hydrogen and carbon dioxide to alcohol (claimed) such as ethanol, propanol, i-butanol and n-butanol.    ADVANTAGE - The method provides very high conversions of hydrogen and carbon monoxide in commercial-scale, continuous operations to alcohol. The efficiency of hydrogen bioconversion in anaerobic processes depends not only on the presence of carbon dioxide in the aqueous fermentation menstruum but also the ratio of electrons to carbon atoms. The method enables use of advantageous syngas sources yet obtains enhanced conversion of the syngas by adjustment of the composition of the syngas by the addition of an additional gas. The adjustment in the composition by the addition of at least one other gas is particularly attractive because all hydrogen and carbon oxides values in the feed gases are available for the bioconversion. Moreover, compositional adjustments can be readily implemented on virtually a real time basis by the blend ratio. Hence, in the event that a unit operation generating syngas has an upset or other process change affecting syngas composition, the electron to carbon (e-/C) ratio can be adjusted quickly to avoid undue loss of syngas values due to the use of less desirable electron to carbon atom ratios.    DETAILED DESCRIPTION - A continuous process for anaerobic bioconversion of gas substrate comprising carbon monoxide, hydrogen and carbon dioxide in aqueous menstruum containing microorganisms suitable for converting substrate to alcohol, involves continuously contacting gas substrate with aqueous menstruum to bioconvert gas substrate to alcohol and providing alcohol-containing menstruum and depleted gas phase; continuously withdrawing depleted gas phase from aqueous menstruum; continuously or intermittently withdrawing a portion of menstruum for recovery of alcohol. The withdrawal is sufficient to maintain the alcohol in the menstruum below concentration that unduly adversely affects the microorganisms, where at least two gases having different compositions are used as gas substrate to provide overall gas substrate having ratio of electrons to carbon atoms in the range of 5.2:1 to 6.8:1.