Solid-state C-13 NMR spectroscopy was used to investigate the chemical shift of nanotube carbons on m- and s-SWNTs (metallic and semiconducting single-walled nanotubes) for samples with widely varying s-SWNT content, including samples highly enriched with nearly 100% m-and s-SWNTs. High-resolution C-13 NMR was found to be a sensitive probe for m- and s-SWNTs in mixed SWNT samples with diameters of similar to 1.3 nm. The two highly enriched m- and s-SWNT samples clearly exhibited features for m- and s-SNWT C-13 nuclei (similar to 123 and 122 ppm, respectively) and were successfully fit with a single Gaussian, while five mixed samples required two Gaussians for a satisfactory fit.