A generalized form of the Peng-Robinson equation of state is used to c
alculate two and three phase equilibria in systems containing dense CO
2 in contact with both well defined hydrocarbons and with reservoir oi
ls. The thermodynamic model combines completely generalized interactio
n parameters and critical property correlations with a truncated form
of a gamma distribution model for describing the hexane plus fraction
of a reservoir oil in a semi-continuous manner. Predictions of phase b
ehaviour in well defined systems are used to demonstrate the accuracy
of the method and are compared to regressed fits of the data. Characte
rization of the C6+ fraction of the reservoir oil requires specificati
on of the nature of the oil (paraffinic, olefinic, naphthenic, or arom
atic), the average molecular weight of the C6+ fraction, and a single
parameter describing the skew of the gamma distribution model. Sensiti
vity of phase behaviour predictions to the above parameters is found t
o be reasonably limited and surprisingly good fits of the data are obt
ained over a wide range of parameter values.