The ministry of Industry has a webpage which tells a user which gas stations are the cheapest in whatever province of Spain and consequently the city of interest. For example checking which gas station was the cheapest in the Las Tablas area of Madrid, I chose  gasoline 95, then the province of  Madrid, location  of Madrid and lastly put in the postal code which resulted in three gas stations. It is that easy!Click here to start saving on gas: http://alturl.com/isnd