On my road trip to Amarillo, the Regal has been returning 28-29 mpg, and that's on mostly E10 gas, 65-75 mph, and the a/c running about 3/4 of the time. Without those hampering effects, it would probably be doing about 30 or a bit more.
Thanks to pure-gas.org, I found an E0 station in Amarillo, right on I-40. Octane for regular was 86, due, no doubt, to the altitude (Amarillo sits at 3700 ft.).