I can't find any new updates on ultra low sulfur diesel in San Carlos or on the way from Nogales. Does anybody know if they or somewhere close has it yet?
UBA diesel other than the state of Baja california exists SOLELY to meet the USA mandate that cross-border "traylors" have ULSD when they cross. Only MAJOR Mexican border crossing towns have UBA. US Customs can tell you if a small border town has UBA available.
Mexico City will get UBA before anywhere else in the country.