Tertiary hydrocarbon miscible flooding is an important enhanced oil recovery process for revitalizing mature, water-flooded, carbonate reservoirs. Over the last 16 years Husky Oil has developed extensive expertise in successfully applying tertiary vertical gravity-stabilized hydrocarbon miscible floods in the Rainbow Basin, Alberta. The combined incremental oil reserves of four major tertiary miscible floods (Keg River B, F, and South E and G pools) are expected to be 25 x 10(6) m(3). This paper presents the design, operation, and three-year actual field performance of st vertical tertiary hydrocarbon miscible flood in the northwest lobe of the Rainbow Keg River F pool. Oil production from the northwest lobe has improved significantly, from less than 100 m(3)/cd during the first few months of miscible flooding to more than 200 m(3)/cd over the past year. This paper discusses major design factors and a sound corresponding operating strategy that have ultimately resulted in the technical and economical success of the vertical tertiary miscible flood scheme. These factors include: 1. Selection of a minimum operating pressure 2. Optimal solvent composition 3. Solvent slug size 4. Critical frontal advancement rate, and 5. Proper placement of solvent slug.