Abstract: The Šandrovac Field is located in the northern part of the Bjelovar Sag (subdepression). Reservoirs in the Šandrovac field are lithologically heterogeneous, containing a considerable amount of CO2, both in solution gas and natural gas. Geostatistical tool used in this thesis is called the variogram. The variogram determines which values of data series on a certain distance are still in correlation. Variograms in this thesis were made using the Variowin computer program. The creation procedure and the parameters of the variogram were described in Chapter 4. In that chapter, the description of the variogram, as well as the description of its parameters and variogram models, used in geostatistics, were given. Furthermore, detailed instructions on the making of variograms using the Variogram computer program accompanied by figures were shown. The data used in the making of variograms, the completed variograms and the approximation of variograms by mathematical models, were shown in Chapter 5. Real data for reservoir and “artificial” data for top were used. Based on that data, first to be made were the porosity histograms of the reservoir and the top. After that, the variance, median as well as minimal and maximal porosity values were calculated. Furthermore, variograms and the approximation of variograms by theoretical models were made. It was concluded that variograms made from data in Chart 5-1 could not be approximated by any theoretical model. Because of that, such sequence (sedimentation) was shown graphically in figures 5-12, 5-13, 5-14 and 5-15. Variograms, which were made from data in Chart 5-2, were approximated by the exponential model.