The present disclosure describes methods and systems, including computer-implemented methods, computer program products, and computer systems, for measuring wettability of a rock sample. One method includes: at each temperature of a plurality of temperatures, obtaining a first Nuclear Magnetic Resonance (NMR) surface relaxation time for a rock sample having a saturation level; determining a first temperature sensitivity based on the first NMR surface relaxation times and corresponding temperatures; at each temperature of the plurality of temperatures, obtaining a second NMR surface relaxation time for the rock sample that is saturated with oil; determining a second temperature sensitivity based on the second NMR surface relaxation times and corresponding temperature; and determining a wettability of the rock sample based on the first temperature sensitivity and the second temperature sensitivity.