Empirical investigations of the EO–firm performance relationship have typically focused on small and medium-sized ventures and have relied on survey data. Will the shape of the relationship curve hold for firms that moved past the ‘ventures’ phase? Our study investigates a sample of 11,843 small, medium, and large publicly listed firms drawn from the COMPUSTAT database. We confirm the existence of a U-shaped EO-performance relationship, and our analysis offers new evidence on the role of EO in SMEs versus large firms. Contrary to conventional wisdom, our sample of SMEs displayed lower levels of EO than large firms, and large firms were found to be five times more likely to have high rather than low levels of EO. Additionally, environmental dynamism was found to influence the U-shaped relationship. We offer a deeper understanding and new insights on the moderating role of environmental dynamism. For example, the U-shaped EO-performance curves for high and low environmental dynamism were found to intersect, contradicting prior arguments that different levels of environmental dynamism will deliver differing EO-performance relationships. Finally, this study offers evidence of the interpretive advantages of using financial proxies to reflect study variables, compared to traditional approaches like surveys.