| Abstract: | We study the relationship between prices and market structure in geographically isolated markets that are exposed to large demand shocks. The temporal variation in market size allows us to overcome the classical endogeneity bias in standard concentration‐performance regressions. We find evidence of local market power in petrol markets due to product differentiation. Additionally, the high margins that characterise concentrated markets dissipate quickly with the number of competitors. Ignoring market structure endogeneity leads to underestimating the effect of market concentration on prices between 55 and 70%. |
