Mass and the energy-capital conservation equations are employed to study the time evolution of the mass of oil and the oil price evolution with time of the resources sold to the market in case of no-accumulation and no-depletion of the resources; i.e. when the resources are extracted and sold to the market at the same mass flow rate. The time evolution of the monthly oil price is studied from 1994 until 2012, investigating the detailed forecast resulting from the application of the present theory. The oil price can be reasonably forecasted using the prime and the discount rate interests as extreme limits