Modern environmentally beneficial methods of formulating motor gasoline often use alcohols and/or ethers as octane improvers, Thus, the thermophysical properties of these substances have become important in process engineering design, the simulation of gasoline blending operations, and engine operability. In all of these applications, phase equilibrium properties are represented by thermodynamic models, which are derived from a combination of theory and experimental data. This work seeks to quantify these models from careful measurement of key thermodynamic properties. Vapour-liquid equilibrium measurements on 2-ethoxy-2-methylpropane (ETBE), 2-methoxy-2-methylbutane (TAME) and 2-methoxy-2-methylpropane (MTBE) with various alkanes, aromatics and oxygenates have been made over a temperature range of 293 to 323 K using a static experimental method. These data are utilised in the development of a flexible model for the thermodynamic properties of motor gasolines. The data are well correlated by the UNIQUAC excess Gibbs model for the liquid phase and with the Hayden-O’Connell correlation for the virial equation for the gas phase. Prediction of the vapour phase composition above a gasoline containing MTBE and methanol show maximum differences of 0.0353 in mass fraction.