This paper presents the results of research on the effects of organizational level and population or industry-level clocks on organizational mortality rates. It reports estimates of a model in which the effect of organizational age varies by organizational size and the effect of density varies by population age. Analysis of data on the mortality experiences of all firms that produced automobiles in Britain, France, Germany, and the United States during 1885–1981 reveals complex patterns of effects of organizational age and size. The results concerning density and population age generally support a recent extension of the theory of density-dependent organizational evolution.