In this paper, we report experimental results that demonstrate the combined effects of variations in interfacial tension (IFT) between one pair of three phases and wettability of a porous medium on three-phase relative permeabilities. We used two analog three-phase systems, in which the IFT between two of the phases could be varied systematically while holding the IFTs between the other pairs of phases approximately constant. We report measured three-phase relative permeabilities for systems with IFTs between two of the three phases varying from 0.005 to 2 mN/m. Phase-recovery and pressure-drop data were interpreted by the combined Welge/ Johnson-Bossler-Naumann (JBN) method to yield relative permeability curves. The results obtained indicate that as IFT between the analog gas/oil pair of phases decreases, relative permeabilities for those phases increase at a given saturation. The relative permeability for the analog water phase remains nearly unchanged for water-wet porous systems, but it decreases especially at low phase saturations for oil-wet porous systems.