A reservoir engineer is concerned with underground oil and gas reserves, specifically finding the most efficient way to extract their resources. The reservoir engineer can work through all phases of a well’s lifespan, from helping petroleum geologists find well sites, through field development, planning, forecasting, testing and drilling. Their duties are varied and can include simulation and surveillance of the well, production forecasting, and development planning. Reservoir engineers are especially concerned with determining the economic viability of a well, finding out how much the well can produce, and making sure that the well is cost effective. They are also responsible for reporting reserve numbers to regulatory agencies. Reservoir engineers are usually petroleum engineers, however occasionally chemical or mechanical engineers can be trained for this position.