Core data from a sidetrack well 250 ft from an old injection well showed intervals of excellent miscible-gas sweep, with miscibleflood residual ail saturations (ROS＇s), S-orm, of approximate to 5% PV. Less-well-swept intervals had intermediate S-orm values. Numerous intervals had not been contacted by miscible injectant (MI). Chromatographic analyses of the Dean-Stark core extracts quantified miscible-gas alteration of the oil and was especially valuable in the interpretation of intermediate oil saturations. Compositional reservoir simulations showed that high-permeability thief zones and a number of thin shales controlled sweep efficiency near the cored well.