Any of you Colorado guys know when they switch to the summer gas?
My gas mileage went up about 1 mpg but I didnt think that they had switched it yet.

Also how many of the other states do the summer/winter thing - anyone know?

 

From what I can find out, the (federal) government mandates switchover no later than June 1, but oil companies may switch over earlier, probably starting around April 1. I don't think there are any state-wide regulations anywhere that are different except in California, but there are special regs in place in large metro areas such as NYC and Chicago.

If your mileage went up, I'd say that the station you used has switched over.