The Rackett equation calculates liquid molar volume for all activity coefficient based and petroleum tuned equation of state based property methods. In thelast category of property methods, the equation is used in conjunction withthe API model. The API model is used for pseudocomponents, while theRackett model is used for real components. (See API Liquid Volume .)Campbell-Thodos is a variation on the Rackett model which allows thecompressibility term Z i *,RA to vary with temperature.