AbstractAlkali oxides added to methanol catalysts increase the formation of ethanol,n‐propanol and isobutyl alcohol. This result has been known for many years, yet few quantitative studies have been reported in the literature. Data obtained on a commercial copper‐zinc oxide catalyst promoted with K2CO3are presented and compared with published work. The optimum promoter concentration was about 0.5% by weight. The H2to CO feed ratio was important in determining the higher alcohol selectivity. The rate of production of isobutyl alcohol varied asp H2−0.7p CO2.2while for methanol, ethanol andn‐propanol both exponents were positive and less than 1.6. Decreasing the hydrogen to carbon monoxide ratio from 2 to 0.5 more than doubled the isobutyl alcohol selectivity. Chain growth schemes predicting the higher alcohol selectivity are presented and estimates of the parameter