Core flooding is an essential test in petroleum engineering labs. The test duration should exceed the duration of the transient pressure (DTP). There are three objectives for this study: (1) to investigate the stages of the DTP of liquid core flooding, (2) to compare the solution of the diffusivity equation with experimental data and (3) to develop a simple empirical equation that can be used to predict the DTP and to identify core heterogeneity. Brine was flooded at different flow rates in sandstone cores with permeabilities ranging from 0.5 to 110 mD. The analysis methodology included calculating the derivative of the pressure gradient with respect to the injected volume. The results showed that the DTP consists of two stages. The liquid compressing is the dominant process in the first stage and the liquid pushing is the dominant process in the second stage. In high-permeability cores, the first stage disappears. The diffusivity equation yielded only the second stage of the DTP with improper short values. The empirical equation was represented by a power function of the permeability, the change in the injection rate and the final injection rate. Two types of core heterogeneity were characterized. © 2012 Nanjing Geophysical Research Institute.