The water-R143a partition coefficients for a set of thirteen organic solutes have been measured using high-pressure spectroscopy. Water partition coefficients of the organic solutes were measured in the gas and supercritical phases of 1,1,1-trifluoroethane (R143a). A linear solvation energy relationship (LSER) was developed to predict the measured water-R143a partition coefficients using the Abraham descriptors of the solute and an additional solvent descriptor as independent variables. Considering the entire water-R143a partition coefficient data, the LSER model has an average absolute relative deviation of 49.5%. Considering only the data above the critical density of R143a, the LSER has an average absolute relative deviation of 40.7%.