I'm proud to announce that this book was selected as a "Best Project of The Year" in Petroleum & Gas Engineering Department by the University of Engineering & Technology Lahore, Pakistan. It contains a detailed knowledge about unconventional energy resource, "The Tight Gas Reservoir" which is today's interest of the market. The book also explores new methods and some extra considerations for reserves estimation in TGRs, as conventional methods do not provide accurate results in such cases. This edition includes special effect called "Gas Slippage Effect" and simulation study of TGRs by using software ECLIPS. It also provide us with a short description of use of software ECLIPS with numerical examples, which is currently used in oil & gas industry.