Reservoir zonation is the most important job in oil industry which dominantly relies on the major properties of rocks. Fundamental properties of rocks are usually understood by their detailed description in the field (lithofacies analysis) and laboratory (petrofacies analysis). The facies (lithofacies and petrofacies) determination in most subsurface studies is impractical, due to lack of cores and cuttings. In such situations, where the wire line logs are the only data available, the logfacies or electrofacies are determined instead. Using multivariate cluster analysis, in this study practiced the logfacies determination on the Asmari Formation of Marun Field by programming a new algorithm with MATLAB software. The study is carried out on the logs of a well in which the Asmari Formation is fully cored. Determined logfacies are correlated with lithofacies defined on the cores and thin sections. Reliability of the procedure in logfacies determination is examined and an appropriate cut off level is defined for the cluster analysis. Result from this study is prepared to use in logfacies determination of the adjacent wells with no cores and cuttings.