A common remedial technology for properties with subsurface soil and groundwater contamination is multiphase extraction (MPE). MPE involves the extraction of contaminated groundwater, free-floating product, and contaminated soil vapor from the subsurface. A network of recovery wells conveys fluids to a vacuum pump and to the treatment system for the contaminated groundwater and soil vapor. This article describes a study of MPE operational data from nine similar remediation projects to determine the most important design parameters. Design equations from guidance manuals were used to estimate the expected radius of influence (ROI) based on measured field data. ROIs were calculated for the vapor flow rate through the subsurface and for the groundwater drawdown caused by the MPE remediation activities. The calculated ROIs were compared to the measured ROIs to corroborate the assumptions made in the calculations. Once it was established that the calculated and field-measured ROIs were comparable, a sensitivity analysis determined ranges of different design and operational parameters that most affected the ROIs. © 2012 Wiley Periodicals, Inc.