Abstract Nowadays, the oil industry is focusing its effort and interest on gas shale reservoirs. Gas shale wells are normally tested by recording the flow rate values under constant pressure conditions. Therefore, time superposition is required in order to conduct transient-rate analysis which normally uses the radial solution of the constant-rate diffusivity equation. This superposition function is also applied indiscriminately to other flow regimes without considering the possibility of an existing error. The literature only reports a case where this situation is dealt with. However, the analysis is performed using curve-decline matching. This study presents the analysis of the effects generated by extending the superposition time function generated with the constant-rate radial solution of the diffusivity equation to other well-known flow regimes. The work consists of performing simulations for the following scenarios: variable rate under constant well-flowing pressure, uncontrolled changes in flow rate, isochronal uncontrolled changes in flow rate, isochronal increasingly changes in flow rate and isochronal decreasingly changes in flow rate. Superposition time functions were generated for each scenario to compare each flow regime (linear, bilinear, elliptical, spherical and pseudosteady state) superposition function to the radial flow superposition function. In general terms, it was found that the generated effects of using the radial time superposition function are negligible. Even, good values of the average reservoir pressure with the radial flow superposition function were obtained. However, it was noted a notorious deviation of the linear and bilinear flow regime tendencies for hydraulically-fractured wells. This leads to erroneous estimation of the fracture parameters.