An account is given of the ore-reserve estimation procedure applied at Sivrihisar sepiolite mine. After a description of the geology of the area a geostatistical study based on 434 composite samples is presented. The composite samples gave a negatively skewed distribution with a mean of 86.09% sepiolite. Experimental variograms representing three main directions-strike plunge, cross-dip and downdip directions-were calculated and a simple spherical-type model was fitted to the variograms. After validation of the model parameters the deposit was divided into blocks and kriged to obtain in-situ grades and tonnage. Finally, the actual grade-tonnage curves were calculated in which the tonnage corresponds to the number of blocks above a series of cutoffs.