<div class="htmlview paragraph">A coaxial cylinder viscometer has been used to determine the theological properties of a hydraulic fluid when contaminated with jet fuel. The viscosity at different pressures, temperatures and shear rates has been investigated. Furthermore, traction measurements between a steel bail and steel plate have been carried out. The results are compared with theoretical predictions. A decrease in oil film thickness due to viscosity loss has been established for fluids containing jet fuel. The pressure-viscosity-coefficient, the viscosity increase with pressure, is not effected by adding jet fuel to the hydraulic fluid.</div>