Compressed air is widely used throughout industry. It is sometimes called the “fourth utility”, after electricity, gas and water.From mining, lumber and paper mills, petroleum, chemical, textile and glass production to small manufacturing plants and hotels, compressed air provides critical services and can often represent the majority of the facility energy costs. Since many facilities cannot function without compressed air, reliability is paramount, but given that sound operating practices can reduce energy consumption by 20% to 50%, efficiency is high on the agenda. This is the first in a series of compressed air system courses offered by Energy University. In this course, we will look at the relative inefficiency of compressed air and examine the components of a compressedairsystem.