An analysis of c r i t i c o l doto far a large number o f binary mixtures of normal fluids shows that the c r i t i c a l temperature and the c r i t i c a l volume con each be expressed as quodratic functions o f the surface froction. Eoch of these functions requires one adiustable parameter characteristic o f the binary pair; for any family of chemical components, these parameters, upon suitable reduction, follow definite trends.It was shown that the surface fraction gives much better correlation than any other size-weighted variable. F o r the c r i t i c a l pressure, however, no quodrotic function wos adequate. T o calculate c r i t i c a l pressures, the correlations for critical temperature ond c r i t i c a l volume were used i n conjunction with o slightly altered version of the Redlich-Kwong equation.Generolizotions to systems containing more than two components follow without addition01 assumptions. The methods presented i n this paper provide good estimates for c r i t i c a l constonts of multicomponent mixtures. These ore porticularly useful for onolyzing and correlating vapor-liquid equilibria i n the c r i t i c o l region.The critical properties of pure fluids have received much work. The critical properties of mixtures, however, are not attention and as a result of much experimental work, dating known nearly as well, although experimental d a t a are availback nearly 100 years (3, 6 ) , a s well a s semiempirical cor-able for a surprisingly large number of binary mixtures (58).relations (561, i t is now possible to make good estimates Critical properties of mixtures are required in petroleum of the critical temperature, pressure, and volume of most and natural g a s engineering and for rational design of seppure fluids encountered in typical chemical engineering aration equipment and chemical reactors at high pressures.