Investigation of lateral heterogeneities (clusters) in cell membranes is an important step toward understanding the physical processes that lead to the formation of lipid domains and rafts. Computer modeling methods represent a powerful tool to attack the problem, since they can detect clusters containing only a few lipid molecules-the situation that still resists characterization with modern experimental techniques. Parameters of clustering depend on lipid composition of a membrane. In this work, we propose a computational method to detect and analyze parts of membrane with different packing densities. A series of one- and two-component fluid systems containing lipids with the same polar heads and different acyl chains, dioleoylphosphatidylcholine (18 : 1) and dipalmitoylphosphatidylcholine (16:0), were studied using molecular dynamics simulations. The method is universal and could be applied to any other membrane system with arbitrary lipid composition. Here, we demonstrated that the studied lipid bilayers reveal small lateral dynamic clusters composed of just several (most often, three) lipid molecules. This seems to be one of the most important reasons determining the "mosaic" nature of the membrane-water interface.