While we are talking about mileage though, there are things besides the obvious (driving style, speed, traffic, etc.) that can affect your MPG from tank to tank.
Summer vs winter fuel standards set by various regulatory bodies.
Air conditioner usage. More AC = less MPG.
Fuel temperature - Retailers never discuss fuel temperature with their customers, but wholesale fuel prices are adjusted at the rack for every degree over/under the standard 60 degree fuel temperature reference. Fuel expands and contracts with temperature changes. A gallon is a gallon, but a gallon of cold fuel has more BTUs than a gallon of hot fuel.
Summer vs winter fuel standards set by various regulatory bodies.
Air conditioner usage. More AC = less MPG.
Fuel temperature - Retailers never discuss fuel temperature with their customers, but wholesale fuel prices are adjusted at the rack for every degree over/under the standard 60 degree fuel temperature reference. Fuel expands and contracts with temperature changes. A gallon is a gallon, but a gallon of cold fuel has more BTUs than a gallon of hot fuel.