THE PETROLEUM PRODUCTION environment provides a unique challenge for corrosion testing in that it is not a controlled chemistry, as a chemical process environment, but is an environment provided by nature, with all the potential variability in phase distribution and chemical composition this implies. Petroleum environments are always complex, and often change during production from a formation, or may change due to production from formations that were not included or anticipated in the original planning for field exploitation. The corrosion test program for petroleum environments must, therefore, account for the environment nature has created with very little ability to alter or control it. In a very real sense the petroleum chemistry environment is a case of what you see is what you get. The primary concern with corrosion testing in petroleum environments is to ensure that what you see is, in fact, what is really in the actual production environment.