To clarify the realistic upstream boundary conditions of hydrodynamic bearings, the oil spread in a complex system of parallel plates including an inlet tube and axial groove is studied by the computational fluid dynamics (CFD) method. The effects of various design parameters including clearance, velocity of bottom plate, and inlet mass flowrate on oil spread-length are presented and explained. By intensive parametric study for these parameters, an empirical expression for the oil spread-length is derived. A groove with blind ends significantly increases the efficiency of the system. A comparison with experimental observation validates the present model as a proper one for accurately solving oil spread in similar systems.