This course will focus on explaining the thermodynamic principals that govern the compression of natural gas. We will review the concept of state energies and the terms that are used to describe them. We will present the Benedict Webb Ruben equation of state and describe how it is used to determine gas properties. After reviewing the thermodynamic fundamentals, we will apply those principles to the compression process. A special emphasis will be placed on reciprocating compression and thermodynamic measures of performance. Real world test data and examples will be used. We will identify the measurable losses in the system and speculate on the unmeasured losses. We will discuss how these losses affect the thermodynamic efficiency. We will also redistribute the compressor efficiency calculator that was made available at the 1996 Gas Machinery Conference. At the conclusion of the course, the attendee should have a better understanding of the thermodynamic principles that govern compression and know how to use those principles to improve unit performance.