A linear material-balance plot constructed based on "P/Z vs. cumulative production" is frequently used to define the Original-Gas-In-Place (OGIP). The defined OGIP is then used to estimate the reserves. However, a linear P/Z plot can only be obtained if the well is producing free gas from a conventional gas reservoir with no water influx. For a coalbed methane well, the tightness and the reactive gas-rock nature deprive the gas of the needed pore spaces and the time for the material-balance to take place. Consequently, a P/Z plot constructed based on the observed apparent pressure-production-time data bends to the right, similar to a P/Z plot of a conventional gas well subject to water influx. Therefore, several authors have proposed to construct a P/Z plot using "Z*" instead of the measured Z values. The values of Z* are calculated using the Z* function. The Z* function allows for calculating Z* values that are smaller than the measured Z values except the value at the initial pressure. The Z* function also allows for calculating Z* values that are decreasing with decreasing pressure. These characteristics allow the otherwise bending curve to converge into a straight line, with the x-axis intercept as the OGIP. This paper presents the results of conducting a material-balance evaluation using the material-balance method proposed by Hsieh et al. and the measured Z values for a coalbed well. As presented in this paper, we found that, such an evaluation method not only revealed the production characteristics of a,coalbed methane well but also provided us with a method for forecasting future production rates. Subsequently, this technique can be used to estimate the gas reserves for a coalbed methane well as illustrated in the example well.