The rheological behaviour of several fully formulated gear oils is characterized: two mineral-based oils, one poly-alpha-olefin, and three ester-based oils. Experimental traction curves were obtained on a mini-traction machine, where the selected gear oils were submitted to numerous traction tests combining several temperatures, contact loads, and rolling speeds. Having obtained the experimental data from the traction tests, it was least-squares fitted to a rheological model (elasto-viscoplastic rheological model) in order to obtain the model's governing parameters: elastic modulus and limiting shear stress and their dependence on pressure and temperature. This study presents both the traction tests results and the fitted rheological parameters, and discusses the similarities and differences between the oils, as well as the influence of the operating conditions on the behaviour of the oil.