The octanol/air partition coefficient (K-OA) is a key parameter used to predict the long-range transport potential (LRTP) of volatile and semivolatile organic compounds and their bioaccumulation in terrestrial biota. Despite the enormous importance of this parameter, reliable K-OA values are not available for volatile methylsiloxanes (VMS). In this study, a method of syringe headspace analysis was developed to determine K-OA values for six common VMS at trace levels. It was found that log K-OA values of any given VMS were linearly related to the reciprocal of the environmental temperature (T) from -3 degrees C to 40 degrees C, whereas at any given T, the log K-OA values of different VMS were linearly related to their molecular mass and normal boiling point temperatures (T-b). Based on those findings, empirical models were developed to predict log K-OA values of methylsiloxanes using T-b (or molecular mass) and T as the only independent variables. The log K-OA values for common VMS at 25 degrees C were in the range from 2.98 (for hexamethyldisiloicane) to 5.77 (for dodecamethylcyclohexasiloxane). Judging from the log K-OA values, these VMS have little potential for long-range transport and deposition to remote surface media and for bioaccumulation in terrestrial biota.