The electrophoretic mobilities of single-walled carbon nanotubes (SWNTs) in agarose gels subjected to negativelycharged covalent functionalization and noncovalent anionic surfactant adsorption are compared using a simplifiedhydrodynamic model. Net charges are calculated on the basis of estimated friction coefficients for cylindrical rodlikeparticles. The effects of functionalization with negatively charged 4-hydroxybenzene diazonium and anionic sodiumcholate are quantified and compared with model predictions. The adsorption of Na+ counterions into the nonionicsurfactant layer adsorbed on SWNTs (Triton-X-405) is shown to induce a positive charge and reverse the mobilityunder select conditions. This effect has not been identified or quantified for nanoparticle systems and may be importantin the processing of these systems.