When I first started driving in Mexico (almost 20 years ago), there were very few Pemex stations. Pemex is the national gasoline comopany of Mexico. The distance between stations could be hours. Now there are so many stations that you hardly have to give it a thought. I always try to keep 1/2 tank of gas however just to be on the safe side.
From time to time, there is NOT a Pemex station. On my trip to the beach recently, it happened that I was ON empty and leaving Tenacatita. A "No fumar" sign (no smoking) alerts one to gasoline. In the USA, you don't hardly even see a person anymore much less a family using a funnel to put the gas in and then the "resident dog", Luis watching the whole operation! It was an interesting operation.......Note that Luis the dog's name is painted upside down..........why? Who knows?