The purpose of this study was to compare the metabolic cost (MC) of running on a land treadmill (TM) at specific inclines with an aquatic treadmill (ATM) at equivalent running speeds with selected jet resistances. Sixteen participants completed two trials on separate days on a TM and ATM. For each trial, subjects either ran against water jet resistances of 0–100% of maximum jet flow capacity in 20% increments (ATM) or inclines of 0–10% in 2% increments (TM). Oxygen consumption (VO2), heart rate (HR), and rating of perceived exertion (RPE) were recorded during each trial. When running at similar speeds with no resistance (jets or incline), ATM yielded lower VO2 than TM (p < .05). Adding 40% jets during ATM matched MC during TM at 0% incline. At 60% jets, ATM MC simulated TM MC while running on a 4% incline. Comparable MC was observed during ATM 80% jets and 8% TM incline, while ATM 100% jets yielded greater MC than TM 10% incline. We concluded the differences in MC during TM incline vs. ATM with jet resistances was likely a result of nonlinear application of drag forces on the torso created by the water velocities of the water jets.