The critical temperatures (T-c) and critical pressures (p(c)) of ternary mixtures of hexane + heptane + octane and octane + nonane + decane were measured by a flow apparatus. The critical points are visually determined by observing the critical opalescence. The expanded uncertainties with 0.95 level of confidence in critical temperature and pressure were estimated to be 0.4 K and 0.01 MPa, respectively. The relative expanded uncertainty with 0.95 level of confidence in mole fraction was estimated to be 0.012. The experimental data are correlated by Cibulkas and Singhs expressions for the ternary contribution.