This research aims to estimate coal resources and analyze how geological conditions influence the accuracy of these estimations at PT. Mutiara Merdeka Jaya. The geological setting of the study area is categorized as simple to moderate, with seam continuity ranging from good to moderate and varying thicknesses across Seams A, B, and C. Data from 48 drill holes, encompassing quality parameters such as Gross as Received (GAR), Ash Content, and Relative Density, were processed using the Ordinary Kriging (OK) method with a spherical variogram model. Model validation using Root Mean Square (RMSE) and the coefficient of determination (R2) reveals distinct accuracy levels: Seam A achieved an RMSE of 0.9907 (R2 = 0.9907), while Seam B and Seam C showed higher variability with RMSE values of 0.5046 and 0.9405, respectively. Manual estimation yielded a total measured resource of 1,670,000 tons, whereas the Ordinary Kriging method produces 651,930.13 tons across all seams. The results confirm that geological complexity, specifically regarding seam thickness and continuity, significantly dictates the precision of resource modelling. This study provides essential insights for optimizing exploration strategies and ensuring reliable resource reporting in coal mining operations.