Re: Winter/summer blends.
In the 90's, when reformulation occurred in California, and Smog Check II which required dyno testing in non-attainment areas, the following changes where made:
1. Sulfar content was lowered.
2. Oxygenates were increased. MTBE was added to fuel and cause gaskets and seals to shrink, resulting in engine fires.
3. Reed vapor pressure limits were lowered. This required a special summer formulation. Prior to this, there was a federal mandate to lower CO
which was done with E10-15. This leaned fuel-air ratio effectively in the early 90's when most automobiles had carburators, without feedback (No 02 sensors or computers), because E-10, etc has less energy than pure gasoline.
There is a difference in winter/summer blends in various parts the US. (You can't have it both was that, summer or winter gas is more costly.)
I remember the prices soaring, post Katrinia and then stabilizing after an EO that allowed fuel to become universal around the country. Prices did for a while, then diverged again.