No gasoline for units

I'm getting the no gasoline for units when I have 12 million units of it.
Also its a large supply unit.
Does it matter if its large or small or mobile?

There are mobile supply units.

There is a limit to what a supply unit can do.
it has to move from base to a unit, then back and to another unit.

Its a capacity issue.
if you have many units you need more supply units.

Well now a supply unit is not getting supplied.

don't know where

Please give us names.

we will look into it.