Originally Posted by attilla1
The answer is "it depends".
Refineries are configured differently, crudes are different and regional product specifications are different at different times of the year.
As mentioned above, denser fuels have more energy per unit volume. Higher octane fuels tend to have lower density, so they tend to have lower energy per unit volume, but they have (by definition) a lower tendency towards preignition.
Probably the biggest driver is ethanol blended in many but not all of the states in the US. Ethanol has only about 70% of the energy per unit volume as gasoline. In states requiring ethanol which is usually blended at 10%, your mileage will be lower because of the lower energy density.
Hope this helps
An oil boiler (refinery engineer)
it's very intersting ! In France we have only two kind of unleaded gasoline SP95 (unleaded gasoline with 95 % octane) and SP98 (unleaded gasoline with 98 % octane). The composition of the 5 or 2 % remaining is function of the oil supplyer and of the oil origin.
I understand the less light coponents are in the gasoline , the best milage you can get. So, to compare with US gasolines, it seems that european ones have more energy, the US octane purcentage is lower than in Europe because US gasoline contains a great part of ethanol.
French gouvernement has just authorized the bioéthanol. Some oil supplyers may began to send it in april. This gasoline will be have a lower energy so ?