Wellbore effects have been recognized as being important in the analysis of pressure-transient tests for many years. Other works have evaluated the effects of wellbore storage and phase redistribution on pressure-transient response, and analysis methods that account for these effects are well known. It is also known, however, that other wellbore phenomena may affect pressure-transient response, but little has been presented that evaluates or generalizes wellbore phenomena in common pressure-transient tests. This paper presents an analysis of generalized wellbore phenomena, including both mass-related and momentum effects, shows how these are incorporated into general solutions of the diffusivity equation, and provides general guidelines for recognizing these effects in pressure-transient data. In addition, it is shown that the phase redistribution formulation for pressure-transient analysis is actually a special case of wellbore mass-related phenomena, which has much wider applicability than previously realized. Besides general methods for accounting for wellbore phenomena, analytical pressure solutions are also presented for several situations, including heating or cooling of wellbore fluids, phase changes in the wellbore, and inertial effects owing to rapid acceleration or deceleration of wellbore fluids.