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The addition of alcohol as an oxygenated compound, affect the vapor pressure of gasoline. In this study, the vapor pressure of isobutanol – isooctane/n-heptane blends were investigated. Vapor-liquid equilibrium data for the binary systems of isobutanol + isooctane/n-heptane were measured at low temperatures ranging from 303.15 to 323.15 K. The measurement was carried out using simple quasistatic ebulliometer. The apparatus validated by comparing the vapor pressure of pure isobutanol, isooctane, and n-heptane with the published data and average absolute deviation (AAD) obtained was less than 0.83%. The vapor pressure of the binary mixtures correlated with the Wilson, Non-random two-liquid (NRTL), and Universal quasichemical (UNIQUAC) models. The AAD for isobutanol + isooctane system were 1.54%, 1.44%, 1.71% respectively and for isobutanol + n-heptane system were 1.73%, 1.65%, 1.99% respectively. The vapor pressure from the experiment for all systems shows a positive deviation from Raoult-s Law that indicates a nonideal solution.