According to the fed Acquisition.gov website, the primary difference between a statement of work (SOW) and a performance work statement (PWS) is a SOW is written to identify the job and direct the contractor specifically how to do it.
“Here’s what we want, and here’s how you’re going to deliver it.”
The SOW thus usually includes a long list of shalls and shall-nots, with detailed descriptions, diagrams, and dissertations of everything involved in the performance of the contract. In a sense, a SOW is not unlike a mil-spec description. Instead of ordering standard, readily available paper clips, the government tells the contractor the size, weight, length, diameter, tensile strength, type of metal, color, number per box, how many striations can be on each clip itself, and … Well, you get the idea.
A PWS, on the other hand, is written incorporating measurable standards that inform the contractor of the government’s desired outcomes. How the contractor achieves those outcomes is up to them. The contractor is thus empowered to use the best commercial practices and its own innovative ideas to achieve the desired results.
A classic example is a grass-cutting contract. The SOW tells the contractor to use a lawn mower and weedeater and do this and that in a specific manner. It includes specs on what to mow, how to mow, when to mow, what equipment to use and how to use it, and how many people are required in what capacity. A PWS simply tells the contractor the grass is to be maintained between 2 to 3 1/2 inches and how success will be measured.