One of the potential applications of ultrafiltration in oleochemical and biodiesel industries is the separation of palm oil and oleic acid from a glycerin-water solution. In this work, the effect of the palm oil concentration (0.001-0.1 g/L), oleic acid concentration (0.003-0.1 g/L), blend of palm oil and oleic acid concentrations, and pH (2-9) of blended palm oil and oleic acid on membrane fouling were studied using a single-stage Hermia's model. A multistage Hermia's model was used to identify the transition time of the fouling mechanism during the ultrafiltration experiment. The single-stage Hermia's model showed that cake formation was most likely to happen as the highest correlation of determination (R-2) was achieved, followed by intermediate blocking, standard blocking and complete blocking regardless of the foulant types, concentration and pH. The multistage Hermia's model was proven to be capable of identifying the fouling mechanism that dominated at a certain experimental time and also of predicting the transition time of each fouling mechanism that occurred during ultrafiltration. Lastly, the finding in the multistage Hermia's model analysis was verified through scanning electron microscopy and further supported by Fourier transform infrared spectroscopy and contact angle measurement. (c) 2012 Elsevier B.V. All rights reserved.