Supercritical fluid extraction with carbon dioxide was performed to extract acetic acid from real and model solutions of cow rumen fluid. Extractions were performed at varying temperature, pressure, solvent flow rate and extraction times for determining the extraction efficiency using a response surface statistical design. Within the range of variables studied, maximum acetic acid recovery of 93% was predicted at 2.0 g CO2/min solvent flow rate, 2150 psi (14.8 MPa), 45 degrees C, and a 5 h extraction time using an initial acetic acid concentration of 92.4 g/L. A volumetric mass transfer coefficient of 2.848 h(-1) at 35 degrees C and 1500 psi (10.3 MPa) was calculated using a two-film linear driving force mass transfer model. The developed statistical model was tested for applicability on an acetic acid-spiked cow rumen fluid giving comparable results to the developed model. Results further showed that higher molecular weight volatile fatty acids such as propionic and butyric acid present in the fluid were preferentially removed before acetic acid extraction. (C) 2014 Elsevier B.V. All rights reserved.