Compositional reservoir simulators are commonly used to estimate the potential incremental hydrocarbon recovery by gas injection processes. Successful design and implementation of these processes rely in part on the accuracy of available simulation tools. This manuscript presents the results of three main research projects related to fluid flow, mass transfer and sorption in the context of enhanced hydrocarbon recovery from conventional and unconventional resources. The results and analyses presented in this work significantly improve our understanding of enhanced oil/gas recovery processes...