Processes for producing citric acid together with microbial cells as well as producing increased yields of citric acid and/or isocitric acid by fermentation are described. Hydrocarbonassimilating microorganisms are employed in media containing hydrocarbons as the main carbon source. The addition of alcohols, such as C1-C20 saturated alcohols, to the medium permits the accumulation of citric acid together with the obtained microbial cells. The addition of ferrocyanides, such as potassium or sodium ferrocyanide, to the medium enhances the yield of isocitric acid, while the addition of monofluoroacetic acid or a salt thereof to the medium enhances the yield of citric acid.