Abstract: A process for preparing saturated carboxylic acids having from 1 to 4 carbon atoms at a reaction temperature of from 100° C. to 400° C. and pressures of from 1.2×105 Pa to 51×105 Pa by gas phase oxidation of saturated and/or unsaturated C4-hydrocarbons, with an oxygen-containing gas and water vapor in the presence of at least one catalyst. The gas leaving the reactor is partly recirculated in a reaction gas circuit. This reaction gas circuit is configured such that part of the organic acids formed in the gas-phase oxidation is taken from the gas leaving the reactor so that the acid content of the recirculated part of the gas leaving the reactor is from 0.01% to 6.0% by volume.