The semivariogram model used in Geostatistical Analyst depends on the properties of the data. The spherical semivariogram is used by default because it is the most popular in both geostatistical literature and software. No statistical advantage is gained by using this model. From mathematical point of view, the Bessel models is recommended because they provide more flexibility in degree of smoothness when modeling a physical process. However, in comparison with the other models available in Geostatistical Analyst, the estimation of the parameters required by both the J- and K- Bessel models is a time-consuming task.