Octylated asphaltenes (OA), and hexane-soluble n-octyl derivatives of asphaltenes, have been used for the determination of more realistic molecular weight averages and molecular weight distributions (MWD) of asphaltenes. Here we report the synthesis and characterization of the Hamaca OA. Both C-13 and elemental analyses show that about five n-octyl groups per 100 carbon atoms are incorporated into Hamaca asphaltenes. When GPC columns are calibrated with monodisperse octylated asphaltene standards (OAS), the M-n value obtained for Hamaca OA was equal to the one measured by VPO. From this information, and from the GPC results and the above calibration, the MW range (50000-300), M-n (2250) and M-w (6000) values were calculated for the above asphaltenes.