You have hit the nail on the head, but I'll elaborate for those people playing along at home.
The price of oil is mainly dependent on the cost to get the last gallon out of the ground. If 90% of the worlds oil can be dug up for $20 a barrel, but that last 10% costs $140/bbl then everyone pays $140/bbl. If you can expand your $20/bbl oil to the whole world's supply then you can lower the price, and the guys sitting on the $140/bbl oil won't be able to make any money. With the consumption rate of oil going up, there is the possibility of the current oil sources not being sufficient, so we'd need to go find some more oil, which would probably be more expensive.