The aim of this study is to find a deeper understanding of the long-neglected oxidation double-peak of reduced guanines (G(red)ODP) produced at a mercury electrode (ME) by the reverse oxidation of the guanine reduction product (G(red)). Although the reduction processes of G moieties at an ME are hidden in the cathodic currents of the background solvent decomposition, and the G reduction process thus cannot be examined directly, the G reduction product (Gred) can be oxidized back to G, yielding an oxidation signal at about 0.2 V (vs. an Ag/AgCl/3 M KCl electrode). Depending on the measurement conditions, the oxidation signal of Gred may assume the form of a single-peak or a double-peak with GI and GII. The cause of the double-peak generation remains unknown. However, the novel approach based on combining elements of chronoamperometry and voltammetry proposes that the G(red)ODP originates from the oxidation of DNA fragments in two different adsorption conformations. The results indicate that the orientation of G residues is controlled by the repulsive interaction after their reduction and from the difference of GI and GII potentials the repulsion energy was estimated. The new findings may find application as a tool to indicate the structural and surface properties of short oligonucleotides with G bases.