Shell Gas - Worst MPG in over a year...

We usually buy Shell gasoline in our home state of New Mexico and usually get pretty good milage (~50 mpg warm weather, ~45 mpg cold weather). Imagine our surprise when on a recent trip to Texas (warm weather) two Shell fill-ups (different stations) gave us 43 and 42 mpg. Upon our return to New Mexico (still warm weather), our first tank of Shell gave us 52 mpg, or about the usual. We usually get worse milage in Texas than in NM but not this much worse. I can only conclude that for some reason the Shell gas we bought in Texas was unusually crappy, while in NM it is OK. This late in the year (November) I imagine both places have "winter blend" gas.

On a different subject, we have found that Shell and Chevron gas give about the same milage here in NM. Don't know about any engine wear difference.

 

As recently exposed in the California gas shortage crisis, just about every state imposes gasoline formulation rules along with federal government rules to stimulate the adoption and use of ethanol production. The effect of these formulations varies for each vehicle. Some folks swear that ethanol increases their mpg in a Prius engine, and others swear it decreases. Detergents are aimed to reduce harmful emissions rather than increase mpgs. Other components of the formulations are also targeting the reduction of emissions with temperature specific (seasonal) blends.