Poly(ethylene terephthalate) (PET) nanocomposites were prepared via melt compounding using a twin-screw extruder at 265 degrees C. Three different types of organomodified clay were melt compounded with PET: a commercial ammonium-modified silicate clay (Cloisite 30B) and specially prepared thermally stable phosphonium- and imidazolium-modified montmorillonites. X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), and thermogravimetric analysis were used to characterize and evaluate the quality of the nanocomposites. To obtain quantitative evaluation of the dispersion level in nanocomposites, statistical analysis of TEM micrographs was performed using a dispersion parameter, D-0.1, based on free-path spacing measurements. The results showed that the ammonium surfactant yielded the best intercalation results in nanocomposites. POLYM. ENG. SCI., 51: 1178-1187, 2011. (C) 2011 Society of Plastics Engineers