Hussain, S., A. A. Malik, K. Shahzad, N. A. Akhthar, N. Ali, and A. Chughtai. 2015. “Factors Influencing the Formation of Producer Gas from Coal and Biomass; A Review”. Journal of the Pakistan Institute of Chemical Engineers 43 (2):133-47. http://piche.org.pk/journal/index.php/jpiche/article/view/197.