Hmm, not sure. Let's see. Before moving to the next tile I have:
540 kg of petroleum
360 kg of oxilite
After moving to the next tile I have:
450 kg of petroleum
270 kg of oxilite
So this seems like a rounding issue, but that's some very strict rounding to make 270/90 == 2
Unless the actual amount inside the tank is 269.9 and the UI is showing the rounded amount, but the actual game logic is using the real value
Edit:
This is silly, it goes both ways - I moved another tile and now I have :
360 kg of petroleum
180 kg of oxilite
And it's still showing 2 tiles left.
So I assume they're using float values to compare the fuel amounts, and the floating point in the end like +-0.000000002 is messing things up.