A rheometer has been designed which is capable of being used in industrial process flows. The advantage of this instrument is that the rheological parameters of a process flow can be measured in a very short time across a frequency range of at least two orders of magnitude in situ and thus eliminates the necessity of removing a sample from the flow and making off line measurements. The body of the rheometer is made from stainless steel and is constructed such that no dead spaces exist that could potentially trap process fluid and lead to fouling or contamination of subsequent measurements. The operation of the instrument is fully computerized and the rheological parameters such as viscosity, storage moduli, or loss moduli can be used as process controls in a feedback system and thus reduce wastage of the fluid being produced. The operation of this rheometer is described and results from measurements of flowing sunflower oil are presented. The instrument shows an excellent level of reproducibility and its ability to capture and release discrete samples is demonstrated. © 2003 American Institute of Physics.