Oil Icon on a unit question

[ago1000]

There are two small icons that appear on units that require the use of oil to indicate the state of the unit with respect to oil. One when the unit has no oil and the other when oil is low. For example, an armor unit, Oil is used for upkeep (1/3 oil off rail) and for movement(1 oil) and attack(2 oil). I find during the game that the oil icon will remain on the unit for several turns even though I have stored oil that turn according to the production screen. The question I have is, do oil units only recover 20% of their oil needs per turn, similar to upgrade/reinforcement replacements and that is why the icon remains?

[AlbertN]

The oil is never stored -per unit-.

The oil icon appears to notify you oil will be consumed if you use that unit.
If it is yellow looking, it notifies you that you're short of oil stock.
If it is red it signals you that you're out of oil (Which is quite relevant as some units as armour cannot attack, and take damage if moved when you're devoid of fuel for them).

[ago1000]

Thanks