Abstract-Three theoretical models of plane flames burning on a cooled porous-plug type of flame-holder are reviewed and compared with experimentally observed relationships between stand-off distance, flame speed and temperature.It is shown that for most practical burners their conductance is large and that for near adiabatic conditions, the order of the non-dimensional stand-off distance ceases to be 0(1), but is O(ln θ) where θ is the non-dimensional activation energy.