DECLUS: a Fortran 77 program for determining optimal spatial declustering weights. Most data collected in the Earth Sciences are clustered preferentially. The clustering may be in high or low “grade” zones or the data may be clustered in areas accessible easily to sampling. Because all statistical and geostatistical analysis requires a distribution that is representative of the entire area of interest, a declustering procedure is necessary. This paper presents a FORTRAN 77 program to compute declustering weights by a modified cell declustering procedure. An example is given and the results are compared to polygonal declustering and global kriging.