Abstract: Method and apparatus for damping oscillatory behavior and reducing the effective time constant incident to reattainment of equilibrium pressure and flow following a change in fluid pressure or flow rate in a liquid chromatography system. The system may include a chromatographic column, a reservoir for a slightly compressible liquid mobile phase, and piston means cooperating with the reservoir and normally driven at a velocity which is constant over a given time interval, for enabling pumping of the mobile liquid phase through the chromatographic column. In accordance with the invention, a transient velocity component is superimposed upon the constant velocity component of the mobile liquid phase caused by the piston motion. The transient velocity component is proportional to the reservoir volume and to the time derivative of pressure in the reservoir. The additionally imparted motion damps the transient oscillations that arise from any pressure change imposed on the slightly compressible liquid phase.