In this paper we discuss various methods for clustering in order to determine estimates of the cluster mass, focusing on the cluster A3581. Using virtual observatory (VO) tools, possible galaxy cluster candidates are selected. Using the Kayes Mixture Model (KMM) algorithm and the Gaussian Mixing Model (GMM), we determine the most likely cluster member candidates. We then compare the results obtained to SIMBADs method of hierarchy. The mass of A 3581 was calculated and checked with literature values. We discuss the sensitivity of the mass determination and show that the GMM provides a very robust method to determine member candidates for cluster A 3581. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) ; http://www.wiley-vch.de/publish/en/journals/alphabeticIndex/2228/?sID=dvarrj3a0uki5bmeroqjkgm866