Each ton of coal can produce 1.5-2 barrels worth of oil equivalent.  If we did this with as much coal as we use in the US every year for power generation (1 billion tons per year) we would be producing 2 billion barrels per year, about half US consumption.

The proven US coal reserves contain could be made into 400-500 billion barrels worth of oil...more than the guestimated reserves of Saudi Arabia...and at an estimated cost of $15-40 per barrel.