The use of biodegradable lubricants based on vegetable oils is receiving increasing attention, being an important area of research, in order to promote products with a reduced environmental impact during their entire life cycle. Compressibility is one of the key properties that should be taken into account to develop efficient hydraulic fluids and gear oils. The isothermal compressibility of four reference fluids, a sunflower base oil and a biodegradable oil up to 50 MPa and from 298.15 K to 373.15 K has been determined. For this aim an experimental device based on a vibrating-tube densimeter was used to obtain the density values. The density values at atmospheric pressure were correlated within an absolute average deviation of 0.07% with the Rackett equation whereas a modified Tait equation was used to correlate the experimental data over all temperatures and at higher pressures. The sunflower base oil analyzed in this work has a slightly lower compressibility than those of the reference oils for hydraulic and two stroke engines applications. Moreover, viscosities from 278.15 K to 373.15 K and the viscosity index (VI) were determined for all the analyzed oils using a SVM 3000 Anton Paar rotational Stabinger viscometer.