B Based on geological data and the formation of the Jatibarang Volkanik reservoar, consists of the natural fractures and has a gradient of pressure is down (depleted) from 0,438 psi/ft become 0,287 psi/ft. While based on data drilling, conventional drilling (overbalanced) which is done on the formation of the Jatibarang Volkanik always have a problem lost circulation and stuck pipe. Thus the formation of Volkanik Jatibarang is suitable candidates for the implementation of the drilling underbalanced.Well \"X\" is started drilling from stretch hole 36\" until 12½” with depth of 80 mMD to 2058.91 mMD, then the drilling on stretch hole 8½” started from the depth of the 444 mMD to start drilling done by the method of underbalanced drilling (UBD), which is the formation of the Jatibarang volkanik, where the pressure of the formation has depleted, and if still do the drilling using conventional (overbalanced method) will cause many problems in the total loss circulation, formation damage and pipe sticking.On the implementation of the operation of the drilling wells \"X\" there are changes in the design of the layout on the unit membranes N2 package, where initially only use 4 units feeds compressor, 2 unit NPU (Nitrogen Processing Unit), and 2 Booster. But on the implementation, conducted by addition, in order to maintain the pressure remains on underbalanced condition at the time of the drilling progress, underbalanced drilling method provides a positive influence to the rate of penetration (ROP), where the rate of penetration (ROP) will be more increased compared with doing the drilling with the conventional method (overbalanced) sothat can speed up the process of drilling. But drilling with underbalanced method more expensive (high cost) than convensional (overbalanced), because drilling with underbalanced method have a more equipment than convensional (overbalanced) drilling