The provision of helical grooves on the surface of a plain journal bearing can improve the stability of a rotor-bearing system. However, the improvement depends on the arrangement of the grooves along the axial length of the bearing. In order to verify this improved stability three types of helical groove bearing and a reference plain journal bearing were investigated. The helical groove journal bearings were: a symmetrical, an asymmetrical and a partial grooved bearing. The bearing test rig was used to measure the oil flow rate, load carrying capacity, power losses, bearing surface temperatures, and stability characteristics. A theoretical model was developed to calculate the load carrying capacity, stiffness and damping coefficients, and stability characteristics of the various types of bearing. The experimental and theoretical results show that at the expense of a reduced load capacity the helical groove bearings are more stable particularly at low eccentricity ratios. However, the experimental observations showed that the partial helical groove bearing is not a practical bearing because the bearing becomes misaligned above certain load. For a given eccentricity ratio and speed the symmetrical bearing ran hotter and with greater power losses in comparison to the other three bearings. At the same eccentricity ratio and speed, the asymmetrical bearing ran at about the same temperature as the plain journal bearing.