A radial piston hydraulic motor has several components involving sliding or rolling interfaces which may encounter tribological problems. Seizure is one of them and it results in complete stoppage of motion between the relatively moving components and has serious consequences in terms of the operation of a hydraulic motor. Extreme running conditions, like low viscosity and high pressure and speed can cause the rupture of lubricating films and this may lead to the seizure of hydraulic motors. The occurrence of seizure often leads to undesirable damage to the motor components and unscheduled maintenance and can prove to be highly expensive. The work reported in this thesis has focused on investigating the mechanisms of seizure and developing suitable tribo test methods for simulating the sliding interfaces of the hydraulic motor. Extensive motor tests have been performed at low viscosity, high pressure and high speed. The results of this work enabled in describing the seizure progression, namely break down of lubricant film, particle entrapment and thermal expansion. Further, tests have been carried out in a rotary tribometer by using a thrust washer conformal test configuration. In this, the influence of area ratio has been studied and this configuration appears to simulate the piston-cylinder contact effectively during boundary lubricated conditions.