A simple and reliable system for determining the solubility and partitioning behavior of liquid fuel components in liquid water up to 250 degrees C has been developed. The system shows good agreement with literature values at ambient temperature for the solubility of toluene and for fuel/water partitioning coefficients (K-fw). Toluene solubility increased similar to 23-fold by raising the temperature from ambient to 200 degrees C but was not affected at ambient temperature by changing the pressure from 1 to 50 bar. The increases in partitioning of benzene, toluene, ethylbenzene, xylenes, and naphthalene from gasoline into liquid water with increasing temperature ranged from 10-fold for benzene to 60-fold for naphthalene when the temperature was raised from ambient to 200 degrees C. Similarly, the increases in partitioning of polycyclic aromatic hydrocarbons from diesel fuel into liquid water ranged from similar to 130-fold for naphthalene to 470-fold for methylnaphthalene when the temperature was raised from ambient to 250 degrees C. The effect of temperature on the partitioning of naphthalene into water from gasoline and from diesel fuel was similar, indicating that the fuel composition had little effect on the fuel/water partitioning behavior.