The potential of membrane technology for the effective separation of carbon dioxide from methane has attracted significant attention over the past decades. Hollow fiber module is the most employed membrane module for gas separation industries with more than 80 percent of market share. In this book, an experimentally validated non-ideal model has been developed and integrated in a process simulator for hollow fiber membrane module, which can be used to evaluate the separation performance and economics of the system. This work was carried out as a part of PhD at Chemical Engineering Department, Universiti Teknologi PETRONAS. This book serves as reference material for students, researchers and engineers working in the field of membrane technology and gas separation.