This paper describes a statistical study of the contribution of theories previously offered by economists to explain differences in the degree of urban decentralization in the U.S. The focus is on a relative comparison of the influence of auto reliance. A regression analysis reveals that a 10 percent reduction in the percentage of households owning one or more autos would reduce the square mile size of an urban area by only 0.5 percent and raise its population density by only 0.7 percent. Factors falling under the categories of "natural evolution" and "flight from blight" exert a far greater magnitude of influence. For instance, a 10 percent reduction in per capita income would reduce the square mile size of an urban area by 11.4 percent and raise its population density by 10.1 percent, while a 10 percent decrease in the percentage central place(s) population poor would reduce the square mile size of an urban area by 2.6 percent and raise its population density by 1.7 percent. A significant increase in urban decentralization will require more than just reduced auto reliance. (Contains 1 figure, 4 tables and 10 footnotes.)