This thesis is concerned with-the development of a comprehensive computer program for the estimation of multicomponent vapor-liquid equilibria in two phase systems at low to moderate pressures. The system which has been developed is referred to as "the KVALUE routines" and it fulfills its intended purpose in that it constitutes a versatile, convenient, and efficient vapor-liquid equilibria package which is suitable for use either alone or in conjunction with other computer programs. The KVALUE routines consist of approximately 2,000 FORTRAN instructions which require 21,454 words of storage when loaded into an IBM 360 Model 44 computer. The KVALUE routines exhibit a number of very desirable features. The most desirable feature of the system lies in its versatility. Multiple routes leading to each of the major thermodynamic and physcial properties allow the user a considerable degree of freedom with respect to the type and quantity of input data which he may provide. The system structure, and the data structure as well, are designed so as to make the package conveniently integrable with other computing systems. An auxiliary program, CURFIT, which is included in the package, should serve as a valuable aid to the user in performing tasks related to data preparation and organization. [...]