Dorian is rated for 31 mpg on the highway. In the first leg of the trip, burning the MTBE-laden fuel we have here in the metromess, he got about 29 mpg. Throughout the rest of the trip, the fuel economy was between 31 and 32 mpg.
Seems to me that any benefit that the extremely toxic MTBE might have in decreasing emissions would be lost because we're burning more fuel. But hey, what do I know? It's only math.