R Reservoir performance describes the character and behavior of hydrocarbon reservoir when the fluid had been produced. It can be presented in the form of the curve charts between time (t) and oil production rate (Qo). The performance can be predicted by using decline curve analysis methods. It is very important to estimated life of the oil production rate of the wells and the oilfield. Decline curve analysis is used to know the estimation of reserves on the BT field. From decline curve analysis, it can predict future oil production rate and cumulative production in this field. Otherwise decline curve analysis will get the value of estimated ultimate recovery, remaining reserves and recovery factor from the BT field. The reason of the author does this analysis is to estimate how long wells in this field can produce oil until its economic limits. BT field until December 2014 has 6 active wells which are BT-01, BT-10, BT-13, BT-15, BT-16 and BT-22. The BT field has production economic limit rate value (Qe) of 30 BOPD. Cumulative production through December 2014 is 39.87 MMSTB with the last rate is 202 BOPD. The BT field still can produce oil economically until June 2050. Analysis of the declining production curve at the current conditions shows the cumulative production from the field is obtained 40.2 MMSTB and remaining reserve is 0.338 MMSTB. Recovery factor of BT field for current conditions is 55.17%.