Process for the liquid phase oxidation of butane to produce acetic acid in which oxygen and butane are reacted in the presence of a cobalt catalyst in a liquid reaction composition in an oxidation reaction zone at a temperature in the reaction zone in the range of 136.degree. to 150.degree. C., while continuously maintaining a concentration of oxygen throughout the reaction zone equivalent to a partial pressure of oxygen greater than two bar. The concentration of cobalt oxidation catalyst in the liquid reaction composition is at least 0.12% by weight cobalt and up to its limit of solubility in the liquid reaction composition.