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In order to quantitatively interpret the previous experimental single electron emission rates (SEERS) obtained by Guile et al (1997), the Richardson/DushmanSchottky (1914) expression is extended by invoking the concept of multiple images of the emitted electron in the naturally occurring or grown oxide layer covering the metal cathode, first proposed by Silvester (1968) in another application. This leads to a new expression for the Schottky barrier lowering term being obtained, involving a converging infinite series of terms, solvable on a computer, and enables the SEERS to be computed for cathodes covered with varying thicknesses of oxide. Numerical agreement between applied theory and experiment is excellent and requires the postulated presence of electron multiplication-avalanching-in the oxide layer. This method can be further applied to the presence of liquid and/or solid dielectric insulation between oxide covered metal electrodes and can take into account the presence of the anode for small electrode spacings.