An isobaric vapor-liquid equilibrium apparatus for elevated pressures was designed and made by the authors. The isobaric vapor-liquid eqilibrium data of three binary systems(isobutene-isoprene
isobutene-chloromethane and isoprene-chloiomethane) and a tertiary system (isobutene-isoprene-chloro-methane at l0.3bar were determined with this apparatus. Experimental data obtained correlated satisfactorily with Martin-Hou Equation of State(81).