The visualization and image analysis techniques developed by the authors for the study of quantifying the dynamic quality of mixing of a single-screw extruder were employed to investigate the mixing performance of screws of different configurations. The mixing quality was quantified by calculating the variances of the light intensity of the bitmap files cropped from the films taken at the screw length of 15D and 17D of a 45-mm screw diameter single-screw extruder. Temperature and screw speed were the two variables studied. While temperature and back pressure were found to have little effect on the mixing quality, screw speed was demonstrated to be a major factor responsible for the mixing fluctuation observed during extrusion. In fact, screw speed and mixing fluctuation appeared to have a relationship that the higher the screw speed, the bigger the fluctuation (i.e., poorer quality of mixing). The experimental results also revealed that the secondary flight of a barrier screw might be essential to improve the quality of mixing. (C) 2009 Wiley Periodicals, Inc. Adv Polym Techn 28: 1-15, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.201.42