A standard barrel of oil is equivalent to 42 gallons. There are 7.48052 gallons in every cubic foot.
To start, we simply multiply 100,000 barrels by 42 to get 4,200,000 gallons of oil. We then divide this by 7.48052 to get 561,458.29 ft3 (cubic feet) of oil.
It is also helpful to know that 1 barrel is equivalent to 5.6146 ft3 (cubic feet). This is verified by looking at the above answer. Obviously, there is rounding involved in such conversions.