I have uploaded Planar6_July3.tz to http://groups.google.com/group/graph_coloring_program (README_July3) . It contains 100 maximal planar graphs of 50 vertices each. The graphs were generated using LEDA's function maximal_planar_graph(graph, number_of_vertices). I applied my graph coloring program "pl" in batch mode (using a perl script) to a directory containing the 100 graphs and it succeeded in finding a proper 4 coloring for EVERY SINGLE GRAPH. Average solution time per graph - about 1 second, of which a large part was probably disk read/writes. Does anyone have a favorite planar graph of <= 50 vertices that I can try my algorithm on? 50 vertices is not very large, but soon I hope to try graphs of 60, 70 or more vertices. I ran fr_layout on the 100 graphs but the resulting layout was not very clear. I think what I really need is a layout on a sphere and a way to look at the sphere from any angle. Does anyone know of such a thing. In the not too distant future I hope to be looking at graphs of up to 100 vertices. Anything but a spherical layout i believe would be too messy. You can find a clear graphical depiction of the algorithm at http://groups.google.com/group/graph_coloring_B1