The hot fuel issue that gathered some steam about 10 yrs ago I believe is still yet to be resolved, things are just quieter now. Producers, at least some, claimed they were making price adjustments to compensate although I don't believe anyone held their feet to the fire on that one.
So what is hot fuel about...the oil/gas companies deliver their product to the retailer at a price based on the fuel being at or around 60 degrees but in fact is usually 80-95 in summer months and of course somewhat less in the winter, although not as low as you might think. For roughly a year I checked temperatures of fuel at the pump, north south and in-between, it was always off temp by wide margins.
Impact your cost per mile...you bet.