Reserve Fuel Tank

 is one of the items that could be bought at the Emendation Station 3500, at $2000 each.

It instantly refuels 25 liters to your fuel tank, or at a price of $80 per liter. As the Propellent Vendor 12000 on the surface refuels at about $1 per liter, Reserve Fuel Tanks are very expensive in comparison in early game. It may be more useful in late game due to the long distances to the surface (assuming teleporters cannot be used because they cause the game to crash). $2000 is negligible in late game and it is always good to have some Reserve Fuel Tanks in case fuel runs out, as this causes an instant game over. Reserve Fuel Tanks must be used manually - if you run out of fuel, you get a game over even if you have Reserve Fuel Tanks.