The performance characteristics of a plain journal bearing are studied theoretically using a thermohydrodynamic analysis of a bearing lubricated by a nonlinear (cubic) fluid model. Experimental investigations are carried out on a simple journal bearing test rig to study the performance of a full journal bearing with different types of non-Newtonian lubricants, including water-based fluid (WBF). Experiments include the measurement of eccentricity ratio, critical speed and stability limit. A comparative study of the bearing performance is carried out by using two oils which have the same zero shear rate viscosity but different Theological behaviour. The results show that the bearing performance of non-Newtonian oil largely depends on the rheological behaviour of the oil. A comparative study of the theory and experiment. © 1992 IOP Publishing Ltd.