Dispersions of sing-le-walled carbon nanotubes in various solvents and aqueous surfactant emulsions were investigated to correlate the degree of dispersion state with Hansen solubility parameters (δ(2)(t) = δ(d)2 + δ(2)(P) + δ(2)(h)). It was found that the nanotubes were dispersed or suspended very well in the solvents with certain dispersive component (δ(d)) values. They were precipitated in the solvents with high polar component (δ(p)) values or hydrogen-bonding component (δ(h)) values. The solvents in the dispersed group occupied a certain region in a 3-dimensional space of three components. The surfactants with a lipophilic group equal to and longer than decyl, containing 9 methylene groups and 1 methyl group, contributed to the dispersion of nanotubes in water. The surfactants in the dispersed group had a lower limit in the dispersive component (δ(d)) of the Hansen parameter. © 2005 Elsevier Inc. All rights reserved.