Unexplained process variability is likened to a ghost wandering freely through the plant spooking the process. Plant experimentation is discussed as a tool for investigating this behavior, alleviating it, and providing information for process improvement. Two different plant experimentation approaches are discussed and compared: PLEX (PLant EXperimentation) and EVOP (EVolutionary OPeration). The PLEX approach is illustrated using a recent case study of a plant process. The results aided in reducing variability, increasing capacity, and improving overall profitability in the plant.