Polyesteramides were prepared by reactive extrusion by a condensation reaction of a fatty dicarboxylic acid [Unichema Pripop (1009 (C36)] or a carboxyl terminated polyamide 12 (CTPA 12) and a dioxazoline coupling agent [(1,3-Phenylene)-bis(2-Oxazoline), (OO)]. The Residence Time Distribution (RTD) was measured using different fillers as in-line ultrasonic detectable tracers and UV detectable reactive or nonreactive tracers. The apparent RTDs measured using ultrasonic detectable tracers were very different. The analysis of the reaction product and comparing RTDs measured using ultrasonic and UV tracers showed that the addition of a tracer had no effect on the reactive system and that most of the ultrasonic tracers did not flow in an identical manner to the reactive system. No direct correlation was obtained between the rheological or rheokinetic behaviors of the monomers or the reactive system and the apparent RTD. The RTD was obtained by using calcium carbonate as in-line ultrasonic detectable tracers and UV detectable reactive or nonreactive tracers.