Is there a fixed percentage of how much of the oil used to frying french fries will stay in the served french fries?
I guess that it depends on things like dimension of the french fries, frying temperature, oil type.
There's too many factors to have a set percentage of oil that will stay, but lets cover a few common things that determine the oil in your final product.
Heat of the oil:
Coating of the fry (or other fried food):
Post frying treatment:
Crowding the pan:
The right oil:
extending @rfusca: The Variety of Potato: