thank you very much for your reply Tiago. unfortunately, I'm having the same issue on a 12.04 machine too: the pre-compiled version of graphtool fetched from the repository does not run betweenness centrality in parallel. Manually compiling the library solves the issue. At this point I believe there's probably something wrong (and stupid) I'm doing somewhere.. I would past you my python code but it won't be of much help since it does not really do much other than reading the graph and calling gt.betweenness() with my graph and my edge weights map. maybe there's some issue with the way I installed the library? Should I install the python-graph-tool package too? thank you again, m. -- View this message in context: http://main-discussion-list-for-the-graph-tool-project.982480.n3.nabble.com/... Sent from the Main discussion list for the graph-tool project mailing list archive at Nabble.com.