The effects of pH, temperature, and organic acid concentration on the partition coefficients for short-chain organic acids were measured in a crude oil/water system. Acetic, propionic, and butyric acids, as probable substrates for microbial souring of oil reservoirs, were used in conjunction with two types of crude oil. Temperatures of 35-75-degrees-C, pH values of 4.0-7.0, and acid concentrations of 10-1000 mg/L were studied. Initial naturally occurring levels of organic acids in the crude oils were also determined. pH had by far the largest effect on the partition coefficient for all three organic acids for both types of oil. At conditions normally seen in an oil reservoir (pH 5-7), the great percentage (85+ %) of these acids were dissolved in the aqueous phase. The log of the partition coefficient K increased approximately linearly with the number of carbon atoms m the acid. It was seen that organic acids are readily available carbon sources for sulfate-reducing bacteria (SRB) at normal reservoir conditions, and that crude oil may provide a source of organic acids in a low-pH, water-flooded reservoir.