Based on previous empirical research, size is perhaps the most powerful explanatory organizational covariate in strategic analysis. We suggest that theoretical arguments about size be examined carefully to specify models with explicit comparison sets and with mechanisms linking size and underlying processes to outcomes. We illustrate the approach here by advancing arguments about scale competition within an organizational population. In this effort, we feature a theoretical model of scale-based selection, which posits that a firm’s chances of survival decrease with its aggregate distance from larger competitors on a transformed size gradient. The model assumes that the appropriate comparison set consists of all contemporaneous similar organizations competing on the basis of scale and operating in a localized geographic setting. We argue that aggregate distance of a focal firm from larger other firms (a specific form of relative position in the size distribution) reflects the extent to which it can capitalize on potential competitive advantages of scale emanating from economic, political, and social processes. Analyzing the mortality rates of large organizations across the entire histories of automobile industries in four major countries provides support for the theory. We discuss the general implications of our findings for strategic and organizational analysis.