We have measured the liquid-liquid equilibria of water + 2,2,4-trimethylpentane and water + toluene separately with the four oxygenates ethanol, 2-methoxy-2-methylpropane (methyl tert-butyl ether or MTBE), 2-methoxy-2-methylbutane (tert-amyl methyl ether or TAME), and 2-methyl-2-butanol(tert-amyl alcohol or TAOH) at 25 degrees C. Ethanol with the water + hydrocarbon systems forms a type 1 liquid-liquid phase diagram, while the other water + hydrocarbon + oxygenate systems we studied-form a type 2 phase diagram. An implication of this is that the addition of ethanol to a water + hydrocarbon mixture leads to a greatly increased solubility of the hydrocarbon in water and water in the hydrocarbon, while the addition of any of the other oxygenates studied leads to no measurable increase in the hydrocarbon solubility in water, and perhaps even a decrease in the solubility. This observation may be important when assessing both the water pollution potential of possible gasoline reformulations and the sensitivity of the gasoline to water. We have found that our experimental data can be accurately correlated with. either the NRTL or UNIQUAC models. Finally, the liquid-liquid UNIFAC model leads to reasonable, qualitatively correct predictions for the liquid-liquid equilibria of the systems studied.