Numerous correlations have been developed between the organic carbon/water partition coefficient KOC and various molecular properties and descriptors, but most notably the octanol/water partition coefficient KOW and water solubility. From an analysis of the theory underlying in this partitioning and an examination of the existing database, it is suggested that the preferred approach is to correlate the quantity log(KOC/KOW), which is essentially the ratio of activity coefficients in octanol and organic carbon, with a molecular property or with log KOW rather than log KOC with log KOW. Such an approach is presented for estimating KOC for hydrophobic chemicals, including an expression of uncertainty limits, based on a correlation derived between log(KOC/KOW) and log KOW. In its simplest form the correlation is that KOC = 0.35KOW subject to variation by a factor of 2.5 in either direction. It is suggested that new experimental data be assessed for consistency and achievement of true equilibrium by comparison...