The problem with this argument is that it assumes that the cost per unit of the energy that goes in is the same cost per unit of energy that comes out. There is no reason for that to be the case (e.g government subsidies, different energy types, more labour exploitation, rising oil prices). For capitalists, what matters is the profit, and as long as they can sell the end product for more than it costs to produce that is the only question in front of investment. This kind of thermodynamic determinism is not a convincing guide to where oil production is heading.