This paper studies the impact of mergers and acquisitions on prices and markups in the Mexico City retail gasoline market following price deregulation. Using a difference-in-differences design, I find that merging stations significantly increased prices and markups relative to non-merging stations. To understand what drives these changes, I estimate a structural model of spatial competition in which stations are differentiated by location along consumers' commuting routes and firms compete on prices. I use the model to decompose price changes into three channels: increased market concentration, changes in marginal costs, and changes in product quality. My counterfactuals reveal that increased concentration accounts for only a small fraction of the observed increases. Instead, stations that switched upstream suppliers after a merger lowered their wholesale costs, accounting for part of the higher markups. The remaining price increases are consistent with improvements in unobserved station quality. These findings highlight that post-merger price increases need not reflect market power, particularly when ownership changes coincide with other operational changes.