The injection of a fluid with a temperature either higher or lower than the in situ reservoir temperature results in a temperature gradient between the injected fluids and the in situ rock and fluids. Relative permeability is a means of characterizing the flow of immiscible fluids through a porous media. The objective of this study is to consider the effect of the steep temperature gradient upon relative permeability. Along these lines, we present a series of imbibition cycle relative permeability measurements which were conducted in 12-inch and 24-inch Berea sandstone fired and unfired cores using Soltrol 170 and CaCl2 brine. The temperature gradient in the 12-inch core was made equal to the temperature gradient in the first 12-inches of the 24-inch core by injecting the fluids at a constant temperature. Four injection temperatures varying from ambient to 300°F were used to conduct the experiments. Variations in the relative permeability curves from the 12-inch core to the 24-inch core were indicative of the effects of the temperature gradient. Experimental results indicate that the irreducible water saturation increased and the residual oil saturation decreased with average temperature. As the injection temperature increased, the computed values of oil and water relative permeability decreased. The difference in the temperature gradient resulted in variations in both the irreducible water saturation and residual oil saturation and suggested that changes in wettability occurred. Both oil and water relative permeabilities decreased at a larger rate with an increasing temperature gradient.