Gas processing relies heavily on proper pump type and capacity for handling hydrocarbon liquids and liquid solvents in processes to treat natural gas and hydrocarbon liquids. The chapter begins with the basic energy equation needed to size pumps and an overview of pump types. The important concept of head is covered and then an extensive discussion of centrifugal pumps is provided. This section includes net positive suction head (NSPH), cavitation, pump performance curves, system curves, and affinity laws. Text then discusses the fundamentals of positive displacement pumps and rotary pumps. The chapter concludes with a comparison of centrifugal and positive-displacement pumps by listing the pros and cons of each type. Using the material in this chapter helps the reader determine proper pump size and power requirements and know-how to avoid common pump problems.