We analyse the effects of a price floor on price wars in the retail market for gasoline. Our theoretical model assumes a Bertrand oligopoly supergame in which firms initially collude by charging the monopolistic price. Once firms detect a deviation from this strategy, they switch to a lower price for a punishment phase (a "price war"" before returning to collusive prices. In 1996, the introduction of a price floor regulation in the Quebec retail market for gasoline serves as a natural experiment with which to test our model. We use a Markov Switching Model with two latent states to simultaneously identify the periods of price-collusion/price-war and estimate the parameters characterizing each state. Results show that the introduction of the price floor reduces the intensity of price wars but raises their expected duration."