The volume flow of poly(butylene terephthalate) (PBT) ofM̄n=19,600,Tm=598 KandTg=316 K,has been measured in an Instron Capillary Rheometer. The elastic modulus of the longitudinal wave, longitudinal volume viscosity, initial longitudinal volume viscosity, and retardation times are described at temperatures above the melting temperature (493 K), and compression rates of ca. 1 to200×10−5 s−1.An increase in longitudinal volume viscosity with decreasing volume deformation, increasing compression rate, and increasing temperature has been observed. The volume flow activation energy decreases as the volume deformation increases.