Project does not manage the inventory of material resources. It assumes you
have an infinite supply and they are available whenever you need them. You
can assign the same materials to many different tasks - I might have 10
tasks that consume fuel, for example - by simply assigning the amount of the
material used to the task in question and project will calculate the costs.
But as far as Project is concerned, there is no such thing as a "remaining
amount" since there is an unlimited supply available in the first place.
That actually makes sense in the real world since you're going to estimate
the resource requirements ahead of time, during the plkanning phase of the
project well before you actually start doing work and consuming resources,
and you'd order enough to cover all your projected needs. You don't start
the planning process with the assumption that you have 100 gallons of fuel
on hand and that's all that you can ever have. As you develop the plan, if
it turns out you need 200 gallons, that's how much you order.
