In this work, the temperature-dependent rheological behavior of un-used and used vegetable cooking oils was evaluated. The unused edible oils (soybean, sunflower, olive, rapeseed, corn, rice and the mixtures soybean + olive and sunflower + olive) presented Newtonian behavior above 10 s(-1) shear rates; the values of viscosity during heating and cooling were similar, indicating that degradation of the oils did not happen at the temperature range studied (10-80 degreesC). After treatment at frying condition (190 degreesC) there was an increase of the edible oils' viscosity, depending on frying time, perhaps due to the increase of saturation of the oil constituents. The rheological behavior of used cooking oils remained Newtonian at shear rates greater than 10 s(-1). (C) 2004 Elsevier Ltd. All rights reserved.