R Reservoir J on the field X is not saturated oil reservoir but under saturated.Therefore the equation of the Material Balance method used is the MaterialBalance equation for the reservoir does not saturate (under saturated), using theequations of the Odeh Havlena method is water drive. On the calculation for thistype of water drive using the equation of edge water drive because drivers of oilthat comes from an aquifer through the side not vertically.On the determination of the type of drive mechanism at Reservoir J Field X usingthe determination of several methods to find out the type of thrust power used onthis reservoir. Some of the methods used, among other methods, the method ofArps J Drive Index, and the Material Balance simulation method. On the methodof calculating the J Jarps method of the recovery factor (RF) is 43%. Then use thevalue of the Index Drive method and the result is WDI bigger than SDI.The results of the calculation of the Original Oil In Place by using the straight linemethod of Materials Balance in the get results through a plot between the value ofthe natural occurring F/Eo on Y axis between We/Eo on X axis on a graphCartesian, the value of the Original Oil In Place of 5,000 million STB. While theresults of the calculation of Material Balance simulation method using the valueof the Original Oil In Place in the get after the results of the simulation softwareon matching histroy Mbal match i.e. of 5,400 million STB.