AbstractRelationships between octanol/water partition coefficients (Kow) and parameters for molecular surface area or molecular volume are examined with new Kowdata determined by the slow‐stirring method. It is shown that Kowvalues of chlorobenzenes (PCBz's) and polychlorinated biphenyls (PCBs) can be described well using a single parameter regression equation. However, separate equations are established for the different groups of compounds. For 18 PCBs a very significant equation was obtained using data for the solvent accessible surface area (SASA) that was calculated according to a full quantum chemical geometry optimization of the chemicals. With a corrected shorthand method for the calculation of the total molecular surface area (TSA) or volume (TMV), also very significant relationships were obtained.An attempt was made to combine the Kowdata for both PCBz's and PCBs within one equation by adding the solvatochromic parameters. However, there remained differences between the experimental and calculated results for the chlorobenzenes and the PCBs.All linear correlations showed a deflection from the calculated values at high molecular areas or volumes which is probably caused by a solubilizing effect of the octanol present in the aqueous phase. Based on these observed deflections we estimate that the octanol/water partition coefficient (log Kow) will not exceed a value of