I don't think there is a problem at all by the sounds of it that seems pretty reasonable and judging by your price I don't think your running all the way empty, the fuel gauge goes REALLY low just remember your fuel light only comes on roughly 7 liters (according to the manual) and your tank has a capacity of around 70 (65 on the books) but has a bit more in the pipes
James
Edit: Also just my personal opinion i went from Shell V-Power to BP and HOLY crap car runs several times better and almost never backfires (4inch exhaust...I know it came with the car)