This reservoir-engineering textbook is a contemporary analysis of primary recovery. It covers rock and fluid properties, reservoir energies, surface separation, laboratory PVT methods, material balance, fluid flow, well deliverability, water influx, reservoir performance, and decline-curve analysis. Using an unified approach, the text includes the full range of reservoir fluids: black oils, volatile oils, gas condensates, wet gases, and dry gases. It also covers the entire range of producing mechanisms, including gas-cap, water-drive, and compaction-drive reservoirs.