Natural convection immersion cooling of two heat sources in a series of parallel interacting cavities filled with FC-72 has been numerically studied. Both low thermal conductivity (i.e. bakelite) and high thermal conductivity substrates (i.e. alumina-ceramic) have been considered. Comparison has been made between single and double heat source configurations. Non-dimensional temperatures and Nusselt numbers of the heat sources have been correlated as a function of the Rayleigh number.