A chemical byproduct obtained from petroleum and natural gas is defined as a petrochemical. The petrochemical industry forms a significant part of our pursuit of economic development, generation of employment and basic needs. It is a vast field that covers several commercial chemicals and polymers. This book is formulated to assist the reader, specifically students and researchers of petroleum science and engineering, in comprehending the mechanics and methodologies. The information provided in this book accompanied by the graphs, tables and examples employed to elucidate them are driven by the fact that this book is targeted mainly at the petroleum science and engineering technologists. It will act as a good source of knowledge for engineers and researchers and even students concerned with vast field of petrochemicals. This book gives valuable and worthwhile insights into the significant chemical reactions and mechanisms. The aim of this book is to serve as an informative, concise and useful source of information.