In this paper the flow field in the clearances bounded by gears lateral sides and bearing blocks internal surfaces of external gear pumps is studied. Firstly, the pressure distribution is determined applying the Laplace equation to the domain limited by two successive teeth profiles, the middle lines of the first and of the last space and the drain circle, and the main leakage paths inside the clearance are evaluated. Then, the leakage flows between the spaces, and between each space and the drain ambient, are calculated considering different boundary conditions and teeth shapes, and the streamlines are highlighted in order to evidence the main leakage paths. The information gathered through this flow field analysis are used to define equivalent conductance for leakage paths, useful to be adopted in simple lumped parameters models, usually applied with the aim to determine the pressure distribution inside pump casing or, for example, gear pumps volumetric efficiency.