The stability analysis of open cavity ﬂows is a problem of great interest in the aeronautical industry. This type of ﬂow can appear, for example, in landing gears or auxiliary power unit conﬁgurations. Open cavity ﬂows is very sensitive to any change in the conﬁguration, either physical (incoming boundary layer, Reynolds or Mach numbers) or geometrical (length to depth and length to width ratio). In this work, we have focused on the eﬀect of geometry and of the Reynolds number on the stability properties of a threedimensional spanwise periodic cavity ﬂow in the incompressible limit. To that end, BiGlobal analysis is used to investigate the instabilities in this conﬁguration. The basic ﬂow is obtained by the numerical integration of the Navier-Stokes equations with laminar boundary layers imposed upstream. The 3D perturbation, assumed to be periodic in the spanwise direction, is obtained as the solution of the global eigenvalue problem. A parametric study has been performed, analyzing the stability of the ﬂow under variation of the Reynolds number, the L/D ratio of the cavity, and the spanwise wavenumber β. For consistency, multidomain high order numerical schemes have been used in all the computations, either basic ﬂow or eigenvalue problems. The results allow to deﬁne the neutral curves in the range of L/D = 1 to L/D = 3. A scaling relating the frequency of the eigenmodes and the length to depth ratio is provided, based on the analysis results.