1. Z.Y.Zulkifli Abdul Majid, Yasmin binti Ahmad Khan, “The Use of Natural Gas As a Fuel for Motorcycles,” Universiti Teknologi Malaysia, Gas Technology Centre (GASTEC).
2. D. Dortmundt and K. Doshi, Recent developments in CO2 removal membrane technology, UOP LLC, 1999.
3. M.A.A. Md Faudzi Mat Isa, Meeting Technical Challenges in Developing High CO2 Gas Feild Offshore, 2009.
4. V. Chandra, Fundamentals of Natural Gas: An International Perspective: PennWell Corporation, 2006.
5. R.L. Busby and I.o.G. Technology, Natural Gas in Nontechnical Language: Pennwell, 1999.