There is no fixed stock, only a flow into current inventory, i.e., reserves. Development outlay per added unit of reserves or capacity is also a proxy for finding cost and resource rent. Worldwide stability of development cost shows oil has not become more scarce since 1955. A simple development model explains observed value-price relations. The rate of interest has little net effect upon the optimal rate of reservoir depletion. Competitive mineral markets do not resemble monopolized markets. The 1970s expropriation of low-cost oil would under competition have increased depletion; monopoly curtailed it.