The invention is directed to methods for improving the recovery of oil from subterranean geological formations, such as unconventional reservoirs. The invention is also directed to methods for evaluating the efficiency of inject-soak-produce gas injection methods for oil recovery in unconventional reservoirs. In one embodiment, a method for evaluating the efficiency of oil recovery from an unconventional reservoir rock sample includes characterizing the rock sample by imaging the rock sample using a nano-CT scanner and/or scanning electron microscopy (SEM); cleaning the rock sample by flowing solvent through it; saturating the rock sample with crude oil; and establishing initial water saturation in the rock sample.