The objective of this work is to identify the role of three-hydrocarbon-phase flow in the displacement of a reservoir oil by light-hydrocar bon-gas mixtures (methane through n-butane). Slim-tube displacements were conducted with several hydrocarbon-gas mixtures. A compositional simulator capable of handling three nonaqueous phases was used to simulate these 1D displacements. Slim-tube experiments show that as dilution with lean gas increases, the displace ments go from first-contact miscible to multicontact miscible to three-phase, 3 phi, immiscible to two-phase, 2 phi, immiscible. Recovery is high (> 85%) at high enrichment, but nonmonotonic with dilution. Simulation results mimic experimental slim-tube recovery and gas-breakthrough behavior qualitatively; especially the increase in oil recovery with increasing methane dilution of the solvent. High oil recoveries in the 3 phi cases appear to be the result of condensation of solvent into the oil, resulting in (1) low oil viscosity and (2) effective displacement of oil by the second liquid phase that forms.