There is a perennial squeeze on ULSD in the USA. The US military uses a surprising amount of ULSD in gas hog Hummers, Oshkosh, and trucks. Hundreds of millions of gallons as a matter of fact.
Pemex has stated dozens and dozens of times: "Until USB is made available to all Pemex gasolineras throughout Mexico there will be no announcement, by us or our franchisees about the availability of UBA in individual gasolineras".
Mexico DF
Estdo de Mexico
Monterrey
Puebla
Guadalajara
El Paso
Valle de Rio Bravo
All have been mentioned as candidates for first dibs on UBA. For sure the city is first and the state of Mexico is 2nd. After that, who knows? My Pemex engineer friends told me: "When you detect MTBE in winter gasoline blends, then you will know this area is a prime candidate for UBA diesel". They also told me that if Venezuela refined UBA diesel, Pemex would buy it from them. The pressure on Pemex is constant harassment against the PRI party by the PRD state and DF governments. The PRD is using the lack of UBA as political leverage.
They cannot even produce UBA Pemex Premium GASOLINE at the much vaunted Salina Cruz Oaxaca refinacion. Not one drop and production was guaranteed sworn on a stack of bibles to begin in 2014. UBA gasoline is a thousand times easier to manufacture than UBA diesel. Heavy Maya crude is much harder to refine into ANYTHING (other than asphalt) than lighter crudes. in an act of desperation Pemex signed a swap for USA fracked crude - 2 bbls of Maya for 1 bbl of Fracked.
Shell's Wilmington Dominguez, Martinez CA. and Deer Park refineries all have giant capacity DELAYED COKER PLANTS which extract a lot of carbon and sulfur out of process feedstock. In 1966 Shell paid the Bechtel Corporation $300,000,000 dollars, for the Martinez refinery "LOP" Light Oil Processing plant. Fifty years later this plant is far and away more modern than subsequently built Mexican refineries. This refinery's Delayed Coker, is located some 2-miles away on the other side of the refinery. On Ca. Hwy 4 near Richmond, is an (independent) COKE processing plant. This is where all the extracted coke is sent to (for making carbon black and other products) Mexico has none of these resources. Stauffer Chemical, removes molten sulfur via insulated tanker from Shell's Sulfur Plant & Treaters. it goes to Richmond where it is converted into H2SO4 sulfuric acid, then shipped back to the Martinez refinery to be used in the LOP alkylation plant to make alkylate. This is an extremely high quality component essential to aviation gasoline. Mexican refineries do not have alkylation plants. Mexico has lots of hydrotreaters, some cat crackers, and GOSRH (gas-oil straight run hydrotreaters).
Hope This Helps