The study investigates implications of a projected growth of commercial air transport demand in the Chicago area for operations at the region's airports. About 95% of commercial air passenger and flight movements in Chicago currently take place at O'Hare International Airport. Serious airport runway and ground access congestion problems are likely to result if this degree of concentration of commercial traffic continues into the mid-1980's. This study considers the increased airport system capacity which could result if a significant portion of the growth of commercial air transport activity were to take place at Chicago Midway Airport in the late 1970's and mid-1980's.