In mobile and stationary applications, axial piston machines are often used as pumps or motors. The paper on hand deals with the pressurization behavior of swash plate axial piston units. The pressurization is influenced amongst others by the pressure on high and low pressure line pHP and pLP and the rotational speed ω, geometric properties, e.g. the dead vol-ume V_dead, the valve plate design and the fluid characteristics (density ρ, viscosity ν, bulk modulus E). In the following a theoretical and an experimental analysis of the pressurization in the piston chamber and the resulting compression work is presented.