Optimized multi-wall carbon nanotubes (MWNT) suspensions in aqueous solution have been obtained by joint use of ultrasonification and surfactant. A simple experimental procedure has been established to efficiently evaluate the dependence of the surfactant concentration on the MWNT concentration stable in suspension. The study of three different surfactants and MWNT provided by three suppliers showed that a threshold surfactant concentration exists above which the MWNT concentration is maximum. Furthermore, it is demonstrated that the maximum MWNT concentration achievable varies from 0.50 to 7.5 g l-1 depending mainly on quality of the MWNT determined by raman spectroscopy analysis.