Two theories have been proposed that differently identify the frequencies of the low-frequency cutoffs of nonthermal continuum radiation. The first of these theories states that the two low-frequency cutoffs occur at the local plasma frequency and R=0 cutoff frequency, with the continuum radiation propagating in the ordinary mode between the cutoffs and a mixture of ordinary and extraordinary mode above the cutoff. The second theory suggests that the two low-frequency cutoffs occur at the local L=0 cutoff frequency and plasma frequency, with the continuum radiation being generated by Cerenkov emission in the Z mode between the local plasma frequency and upper hybrid resonance frequency. Mode coupling at the local plasma frequency was suggested to generate continuum radiation in the ordinary mode which freely propagates to remote regions of the magnetosphere. In this paper, several examples of continuum radiation observed in the outer magnetosphere by Imp 6 and ISEE 1 are analyzed in detail, and it is shown that these cutoff frequencies occur at the local palsma frequency and R=0 cutoff frequency. In addition, no substantive evidence is found in the outer magnetosphere for a component of continuum radiation propagating in the Z mode.