Understanding the mechanics of fiber attrition during the extrusion process is highly important in predicting the strength of long fiber-reinforced thermoplastics composites. However, little work has been done to investigate the mechanics of fiber dispersion and its effects on fiber attrition. This study investigates fiber dispersion during the extrusion process of LFT pellets. In order to validate our modeling approach, two new fiber dispersion measurement techniques were developed using micro-CT tomography. LFT samples were then subjected to simple shear flow using a sliding plate rheometer and Couette rheometer. Based on the findings, a time-dependent dispersion model is proposed and validated using experimental data. A dispersion model is then proposed for single screw extruders to predict fiber dispersion. Screw pull-out experiments were performed to determine fiber dispersion along a single screw extruder. The model predicts fiber dispersion due to hydrodynamic stresses along the helical length of the screw geometry. Results showed good agreement with experimental measurements. Fiber length measurements were also performed on samples taken from the screw pull-out experiments. Results indicate that both dispersion and breakage occur simultaneously after a critical point of melting has occurred.