Airport cities – concentrations of employment – may have emerged near the major airports of large metropolitan areas. As the U.S. economy is nearly three times as air-intensive as it was in the 1950s, the “aerotropolis” thesis holds that airport cities are a direct consequence of increased air-intensity. The “urban land” thesis holds that airport cities are artifacts of land use changes brought about by metropolitan growth and employment suburbanization. Analysis using Census small area employment data for the 51 largest U.S. metropolitan regions found airport city employment to be one-third to one-half as large as that in CBDs, depending upon the spatial operationalization used. The size of airport city employment was unrelated to metropolitan aviation-intensity but was negatively related to distance from the CBD. The sectors represented indicate that airport cities are comprised of transportation-providing employment, some transportation-supporting employment, but not the concentration of transportation-using employment central to the aerotropolis thesis.