Although some limitations of the original models persist in PORO (flow in parallel no communicating areally homogeneous layers, constant water saturation, Sw conservative tracer travelling jointly with the bulk water flow and steady state flow) it constitutes an advancement in the sense that it incorporates very common aspects of the reservoirs, such as non-regular unbalanced patterns, anisotropy and sealing faults. Also, it is important to highlight that the model may be easily extended for incorporating adsorption, radioactive decay and tracer partitioning in the same way as in the Abbaszadeh-Dehghani and Brigham model

[35, 36] and also it can incorporate the transport of tracers in stationary gas flow [40].