Research in understanding the mechanisms behind driving forces in the fully filled nonintermeshing twin screw extruder concentrated on experimental analysis of the relation between stagger, screw speed, and cross-channel flow due to measured pressure differential in the nip region. A new measure of the pressure driving force was also sought out, to correlate new data to previous findings from visual studies. The first part of the study was to obtain the values for the dynamic pressure on both sides of the nip region. Further refinements to the equipment used in previous studies allowed closer placement of the transducers in the nip region. After the data were stored, analysis started by determining the Ap values from the trace of the pressure differential. By plotting these values, we obtain a highly repeatable curve confirming that the greatest pressure flow occurs at small staggers. A simple 2-D model for pressure flow in the nip region was used to estimate the effect of the cross-channel pressure differential. Values for the cross-channel pressure flow were calculated and compared with the drag flow and found to be significant.