Wellhead production is all oil which exits the ground (wellhead). When the crude oil has been brought to the surface, it requires further treatment so that it can be sent to refineries for processing. The oil produced at the well-head varies considerably from field to field, due not only to the physical characteristics, but also to the amount of gas and water which it contains. Before the oil can be sold, the remaining gas, water and other impurities need to be removed. Once this is done, the oil is stored at the terminal before transport to refineries. It is at this point that the produced oil becomes marketable (production)....