The absolute viscosities and densities of five lubricant base fluids (unformulated) were determined at pressures to 150,000 psig and temperatures to 300 F with a falling weight viscometer. The lubricants investigated were a sebacate ester, a TMP ester, SAE 20 mineral oil, a 5P4E polyphenyl ether, and a methyl chlorophenyl silicone. The falling weight viscometer and experimental procedures are discussed. Measured properties of the sebacate ester are in excellent agreement with the results of previous investigators. Computergraphics generated equations of viscosity, density, and pressure coefficient of viscosity vs pressure at each temperature are presented.Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference held in Miami Beach, Florida, October 21–23, 1975