Field "ED" is located in the offshore of Mahakam Delta, Kutai Basin. This field has two wells, namely D-1 and D-2, also 3-D seismic data post-stack, partial-stack seismic data, near and far. Based on well data, this field has thin reservoirs, which is limited by the D Upper and D Lower horizons. The reservoir is also quite heterogenic because of deltaic environment. With this field condition, the method that is considered appropriate for evaluating the Field "ED" is geostatistic inversion method where the method will produce more detailed picture because it uses a geostatistic approach and continuous simulation with a combination of SGS (Sequential Gaussian Simulation) and Bayesian methods. In other words, the purpose of this study is to characterize the reservoir in the interest zone and obtain the subsurface model by comparing the results of deterministic inversion and geostatistic inversion. The method is doing an acoustic impedance inversion with deterministic and geostatistic method. From the results of inversion, the sandstone and shale, with interbedded limestone are distributed in the interest zone. Also the geostatistic inversion result shows that the layers are thinner than the deterministic inversion result and it is closer to geological condition. In addition to inversion, fluid factor analysis is carried out by using partial-stack seismic data and there is strong amplitude in the interest zone which is indicating the presence of gas.