I do not believe there is a set number that anyone person can determine. And even if such a number could be calculated, there are too many variables for it to stay the same for long.
Regulations, the cost of labor, steel, competition in Natural gas for the same equipment, labor, etc.
If the price of natural gas climbs drastically due to regulations against coal power plants, the drilling rigs will swing from oil searching to gas, just as they went to oil in the past 5 years.
I think under current conditions, $80/barrel will lead to an expanding domestic oil supply, for now.
Thanks. I believe that number is correct as well. Do you have any data on the numbers for other countries? Would a price that low harm Iran?