Better gas mileage by filling the tank when you fuel up?

Do you get better gas mileage by filling the tank when you fuel up? or it is the same gas mileage when you only get a specific amount (ex. $20)?

You know I have to ask? Do you get better gas mileage with higher octane gas? Some cars recommend it, if you fuel up with a higher octane than recommended are you just wasting money?Better gas mileage by filling the tank when you fuel up?
you get the same milage with a small amount of gas in the tank,or full tank!! it's the shape of the tank that make people think they get less millage,thats because the tank is usually smaller at the bottom,the more gas in the tank the better,for keeping the fuel pump pickup tube covered in tuel,and the less chance,of moisture buildup,due to the condensation of metal tank's,also helps prevent rust from forming if ur car has to sit for a period of time..use the octane recamended for ur car,and if u got money for higher octane fuel,i'd buy that once in a while,it's a better grade of gas;if ti's a performance vehichle i'd use premium as much as possable...
the mileage is the same no matter how full the tank and octane is for anti-ping aka pre-ignition if you can drive your car without hearing a rattle or pinging on acceleration esp. on hills at a lower octane dont waste the money on higher octane the increase in fuel mileage doesnt cover the increase in costBetter gas mileage by filling the tank when you fuel up?
wont matter Howe much fuel you put in. the level in the tank has no bearing on the mileage you will get, as for higher octane.yes it burns more efficiently and you will see a slight increase in mileage but not enough to warrant the higher cost up side of high octane is better engine performance.the reason manufactures recommend higher octane is because of the high performance engin,s they put in the there bigger cars need it to run like they tell you it will .and to protect the life of the engin .
if your car recommends regular and you use a higher octane, your wasting your mone, because your computer is set to run on the recomended octane, and as for do you get better milage if you fill up, not necessary, because if your car is going to be easy on gas, then it will be on a half tank as it is on a full tank.Better gas mileage by filling the tank when you fuel up?
You won't get better mileage by filling the tank, but you will get a more acurate reading from full to empty if you are trying to keep track of MPG.

I have to disagree with a lot of the answers here about upgrading to premium vs regular unleaded, but that may depend on where you live. Several auto manufactures have done tests on fuel quality, and found that the amount of water and impurities is much higher here in the southeast (thus our cheaper gas prices), and has caused a higher failure rate on emission and fuel related parts. The extra $4 or $5 a tank is cheap insurance compared to a pricey repair. I personally only fill up with premium and am getting exceptional gas mileage in my PT Cruiser, and I finally convinced hubby to try it for two months in his Toyota Tacoma, and he is very happy with his fuel economy, let alone not having the "pinging" noise the Tacomas are known for.
beter millage with tank full fuel and also go for the super unlead (BP)
Use the type fuel that is recommended for your vehicle. Any higher grade on a regular basis is just throwing your money away, because the gain in mileage is not great enough to warrant it.

As far as better mileage when you fill up, filling up is the 'only' way that you can tell accurately what your mileage is. It is the only way that you will know that there is exactly the same quantity of fuel in the vehicle each time.
you might not see it in your gas mileage but it will keep your motor in better shape and might give you a slight boost of power like maybe one