better gas?

since I have to fill my tank about every 4 trips to work.
I work in surrey so I commute about 120k/day.
I have started keeping track of the millage.
now I am comparing gas stations with the milage I am getting.
so far I am getting interesting results.

from petrocan can I drive about 495Km for about 36 litres, 7.2 lit/100km (13.9km/lt)

now, cause of the blackout I had to get Gas at Shell,
the first tank lasted, 485Km for 32litres, 6.6 lit/100km (15.2KM/lt)

thats roughly an 9% savings going to shell!! over petrocan.

now that shell gas was not pure shell gas, I still had some petrolcan in the tank from the last fill, so I am interested in tomorrows millage.

now there is also an adverse effect to using the shell gas. I notice the car has less power when using shell gas. I expected this though, cause of the performance vs endurance. do not go hand in hand. you have to give up some power to get a better millage.

for the next tank I am going to try out Chevron. and see.