Latest figure I read was something like 3M strays in Michigan. That's just about 2M gallons, or about 200K barrels of oil equivalent (42 gallons per barrel, of which about 9.5 gallons are diesel).
Let's say for the sake of argument that the average stray cat population in each state is 3M as well. That gives us a generous estimate of 10M barrels of cat oil (without the gasoline and so on).
Not that big a find.