The changes in wheel-rail traction coefficients under wet and oil-contaminated rail surfaces are evaluated using the state-of-the-art Virginia Tech-Federal Railroad Administration (VT-FRA) roller rig. This one-fourth scaled test rig provides a controlled environment to measure real-time contact forces under pre-defined conditions. In addition, the rig is equipped with a high-precision fluid dispenser to apply the exact amount of fluids onto the rolling surfaces. Two series of experiments are conducted with water and oil applied individually at the wheel-rail contact with 0.02cc, 0.10cc, and 0.50cc, using a precise dispensing system at a low flow rate of 0.3cc/min, a medium flow rate of 1.5cc/min, and a high flow rate of 7.5cc/min, respectively. The tests include three or fewer cycles of water or oil applications for 4.1s under stable traction conditions. All other test conditions, including creepage, duration, and wheel load, are maintained unchanged throughout the tests, to focus on the effect of water on traction values. The results indicate a high correlation between the amount of water or oil applied to the surface and reduction in traction, in some cases for a short duration and in some over a long period of time. For low and medium flow rates of water, traction reduces immediately upon the application of water but recovers quickly after a short duration to nearly the same level as the dry condition. The duration of reduced traction is directly proportional to the volume of water. A distinctly different result is observed for oil. Even a small amount of oil (0.3cc/min) causes a significant reduction in traction that prolongs over an extended period of time. For the medium application of oil (1.5cc/min), traction remains low for a long period of time and only recovers to approximately 1/2 of the dry condition. For high oil application (7.5cc/min), traction remains extremely low (approximately 1/5 of dry condition) for the duration of the test and does not show any indication of recovery. Oil residue can be felt at the running surface when rubbing a finger over the roller surface. The results indicate that both water and oil cause a significant reduction in traction, with traction recovering to its dry level shortly after the source of water (i.e., rain) stops. When oil is applied to the rail, even a small amount can significantly diminish traction for a prolonged period of time. This is attributed to the possible seasoning of the rail due to oil.