A new, simpler ebulliometer has been developed to accurately measure the vapor pressure of ethanol-isooctane and 1-butanol-isooctane systems at various mixture compositions. The reliability of the experimental apparatus was validated by comparing the experimental data with published data for pure isooctane and ethanol and ethanol-isooctane system. Our data were in good agreement with the published data, with a deviation of less than 1.9%. The vapor pressure of an ethanol-isooctane mixture was initially elevated by the addition of ethanol until the ethanol concentration reached 0.3 mass fractions, then dropped at concentrations above 0.7 mass fractions. For a 1-butanol-isooctane system, the vapor pressure decreased with increasing 1-butanol concentrations. The experimental data were correlated using the Wilson, Non-Random Two-Liquid (NRTL), and Universal Quasi-Chemical (UNIQUAC) activity coefficient models with an average absolute deviation in the vapor pressures of 3.5%, 3.3%, and 6.1%, respectively. (c) 2013 Elsevier Ltd. All rights reserved.