[JackG]

Gas is stored in underground tanks... which automatically regulates the temperature of the gas. On 100 degree days, you're not buying 100 degree gas, just like the gas isn't 0 degrees when the outside temp is 0.

From an edu website: "If you take the average yearly temperature (see Table 1) of an area, that will approximately give the constant ground temperature at about 30 feet below the surface of the ground in an area which is exposed to the sky."

In other words, if you live in the north, you get a better deal, year-round. If you live in the warmer south, you don't do as well. But there's probably little actual difference from month to month in the same area... at least not as much as that article leads you to believe. And especially not day to day, as the earth many feet down from the surface simply can't react that fast.