Someone near Tulum said a Canadian friend had a 50 gallon supplementary tank...
CAMPFIRE TALE
At Aduana right at the border is the ONLY PLACE in Mexico the Aduaneros check for illegally imported gasoline in STORAGE tanks, jerry cans, drums, etc. A tank connected to a vehicle fuel system is absolutely exempt. Quicksilver has a pair of HUNDRED FIFTY GALLON TANKS, with the liter capacity written on thermo tape and pasted right next to the 2" commercial fill necks.
Spreaders of ridiculous tales, don't even bother to check for obvious flaws in their whoppers. Near Tulum who the hell can prove where when how and why the fuel was purchased? At the border fuel is either confiscated (rare) or the vehicle is turned around to re-enter the USA. No filled gas containers allowed.
The entire state of Baja California, every last Pemex gasolinera has ULSD and not only that, every last drop of Magna, and Premium is also refined in the USA. Southbound once you pass the B.C.S. state line, diesel is Mexican refined, Magna is almost always a product of the Salina Cruz, Oaxaca refinacion, but every last of Premium sold in la republica is refined in the USA.
Garitas with a commercial entrance to the USA require USA ULSD be available for varying distances from the garita. Cross border trucking companies are notified which stations have UBA diesel. There is no signage.
It is pure unmitigated B.S. that ULSD (UBA) is available in Mexico (DF) or Monterrey. Only the state of B.C. and a select few gasolineras near garitas have UBA diesel.
Wanna chew on something? Mexican Magna has FIVE TIMES the PPM of sulfur that USA gasoline is permitted to have. Pemex does not place the letters UBA on gasolinera Premium signage for the heck of it. Part of the grand dream scheme is for Mexico (DF) to ban all but UBA gasoline sales not only in the Distrito Federal but the state of Mexico as well. Gobernacion wants everything to change to UBA. Good Luck.