Two widely used commercial cationic liposome formulations, Lipofectamine and Escort, were evaluated for drug delivery efficacy with capillary electrophoresis coupled with laser-induced fluorescence detection using a fluorescein conjugated 2'-O-methyl-phosphorothioate (Me-PS) antisense oligonucleotide and the HeLa cell line. Binding constants were estimated by monitoring changes in the electrophoretic mobility of the oligonucleotide with the liposome solution in the running buffer. From these changes in mobility, the binding constants for Lipofectamine and Escort liposomes with Me-PS oligomer were estimated to be 1139 and 590 M(-1), respectively. Additionally, intracellular concentrations and gene expression were quantified for the liposome formulations.