Reservoir Engineers are involved in every stage of an oil fields life cycle. At the exploration stage they work with the geologists and geoscientists to understand the potential rates and fluid types that could be present in a oil and gas formation. They work with Drilling engineers after this to decide where best to drill the initial exploration well. If this find oil they use the pressure response, rates and fluid type to decide where to drill the other appraisal wells. They then work with economists and project engineers to design the best facilities and top sides for an economic project. To understand what the field will produce in its lifetime, reservoir engineers adapt geological models to see how the hydrocarbons will move through the reservoir. Once the field begins produce reservoir engineering work to maintain the pressure in the field by injecting gas or water.