There is a need to determine the equilibrium partition coefficient of volatile organic chemicals between octan-1-ol and the gas phase, K-OA, because it is being used to assess the potential for respiratory elimination from air-breathing organisms. Here we test the suitability of the variable phase ratio headspace technique for determining the K-OA of volatile organic substances, using acetone, acetonitrile, ethyl acetate, 1,2-dichloroethane, propan-1-ol, butan-1-ol, p-xylene, trans-decalin, 1,3-dichlorobenzene, and 1,2,3,4-tetramethyl-benzene as test substances. The method was found capable of measuring K-OA values at temperatures between 40 and 110 degrees C in the range from 50 to 2000 with a relative standard error of approximately 8%. This allowed for the derivation of K-OA values at 25 degrees C below 10 000. Higher K-OA values close to the threshold for respiratory elimination of 100 000 cannot be determined reliably with this method.