In reservoir evaluation of unconventional reservoirs, engineers use rate transient analysis (RTA) to assess the performance of hydraulically fractured horizontal wells. This technique consists of plotting rate- normalized pressure drop at the well sandface versus square root of time (i.e., linear flow) to calculate the reservoir effective permeability. In this paper, we report on the use of an in-house multiphase numerical simulator applied to production data from several Eagle Ford wells to assess both single- and multi-phase production performance. Furthermore, a combination of numerical simulation and analytical solution techniques was used to validate the information obtained from the RTA in the Eagle Ford wells. This procedure further improved our insight into the flow behavior of unconventional reservoirs. The multi-phase effective permeability calculated from the RTA was within a few percent of the input data to the numerical model. Furthermore, the multi-phase RTA results produce more accurate than the conventional single-phase RTA approach; and the multi-phase analysis results were more in line with the well performance observations than with when using the single-phase analysis approach. Furthermore, the multiphase results were more consistent with the success or failure of the hydraulic fracturing process.