<p><em>YS reservoir has </em><em>data of gas initial in place (GIIP)</em><em> with a volumetric method of 3,476 B</em><em>scf</em><em>. </em><em>Because of improvement of data, GIIP</em><em> </em><em>can be</em><em> </em><em>evaluated using material balance method</em><em>.</em><em> Then the production of wet gas will be forcasted with plateu rate of 40 Mscf/d. </em><em>The PV</em><em>T</em><em> data that needs to be calculated in this study is the gas </em><em>and water </em><em>compressibility factor and the formation volume factor </em><em>each</em><em> year. In determining the type </em><em>of drive mechanism</em><em>, a plot of P / Z versus cumulative gas production is carried out, from the analysis</em><em>, </em><em>the type of </em><em>drive mechanism is</em><em> water drive, it is necessary to calculate the water influx, the method used is the </em><em>Van Everdengen-Hurst</em><em> method</em><em>. </em><em>After all the required parameters are available, the calculation of the initial gas in place will be calculated, the method used is the material balance method and the straight line material balance method.</em><em> </em><em>The results of the</em><em> initial gas in place</em><em> calculation using the material balance and straight line material balance methods are </em><em>3,430 Bscf and 3,428 Bscf</em><em>. If the results of the material balance method and the straight line material balance method are compared with </em><em>available GIIP volumetric method data</em><em>, the percent difference is </em><em>1,32</em><em>% and </em><em>1,37</em><em>%. It can be said that </em><em>GIIP result using </em><em>the material balance method and the straight line material balance method</em><em> </em><em>is accurate because after being evaluated using </em><em>volumetric</em><em> method, it only has a small percentage difference.</em><em> </em><em>Then from </em><em>calculation, </em><em>recovery factor </em><em>are</em><em> </em><em>67,43% using gas initial in place of straight line material balance method. With remaining reserve of 16,532 MMscf, the time of production plateu with 40 Mscf/d is 12,40 months.</em></p>