A method of determining wettability of a rock sample, such as from a core sample is described. The sample is preferably crushed or comminuted to a particulate size where micro fractures have been eliminated, but where the particles are still large enough to represent the native rock matrix and texture. The comminuted core sample is exposed to a test fluid for a given period of time. The rock sample can be split into many separate aliquots, and a series of tests is performed using a series of different fluids and/or the same fluid for different exposure times. The excess test fluid residing on the surfaces of sample particles is removed. The test fluid imbibed into the interior of the particulate sample is then measured. The test fluid can be, for example, water, a non-aqueous fluid, and/or a solution of miscible solvents. The technique used to measure the imbibed fluid depends on the solvent (imbibing fluid) being studied. In one example, this technique includes both gravimetric determination and quantitative chemical analysis. The detection of water can be via Karl Fischer titration.