Price coordination in the Spanish oil market: The monday effect

Spanish premium oil operators have been accused of coordinating gasoline price cuts on Mondays. The objective of this practice, known as the “Monday effect” was to lower the official prices of automotive fuels - that was collected on Mondays - so as Spain was not at the top of the European price ranking. This behavior presumably ceased in May 2013 when Government began to consider the average prices of the entire week instead of Mondays prices. In order to test whether this anticompetitive behavior existed and ceased after the change in the data collection methodology, we employ a novel database that includes retail prices for all petrol stations in Spain in the period 2012–2013. Using a difference-in-difference estimator, we exploit this regulatory change to econometrically identify and confirm that: i) the three main companies, with 70% of the market share, have systematically established lower prices on Mondays, and that this is unjustified by either cost or demand; ii) this price reduction was small during 2012, but increased significantly in the first half of 2013. iii) following the change in the collection of price data by the government, the average Monday effect ‘disappeared’ from the Spanish gasoline market. Our results highlight the price coordination capacity of dominant oil operators in Spain and suggest that authorities that monitor cartels should be much more active in promoting competition in this sector, for example, by facilitating the entry of low-cost or independent stations and/or by being particularly alert to evidence of collusive behavior. Likewise, this coordination capacity must be taken into account when evaluating mergers in this sector and/or imposing fines.