From voltammetric studies, trigonal phase selenium (t-Se) nanotubes, which are bundles of hexagonally packed helical chains of Se atoms, have been shown by others to be stable in acid and have a double-layer region extending from -0.2 (standard hydrogen electrode) to 0.75 V. This is broader than the similar to 0.4 to similar to 0.7 V double layer for platinum and presents a potential range that might allow oxygen reduction activity. This paper presents theoretical predictions of oxygen reduction mechanisms on t-Se. Adsorption energies from Gaussian cluster hybrid density functional and Vienna ab initio simulation program density functional calculations are used in the linear Gibbs energy relationship to predict the reversible potentials for the one-electron reduction steps during the four-electron reduction of O-2 to water, which ideally occurs at 1.229 V. Adsorption energies for reduction intermediates are calculated using single-chain models. Calculated reversible potentials for the four reduction steps lead to the prediction that the step with the highest overpotential is the reductive elimination of OH(ads) to form water and occurs at about 0.8 V. The overall behavior predicted for t-Se is similar to that of platinum, and it is suggested that t-Se is worthy of trials as a potential oxygen cathode electrocatalyst. (C) 2009 The Electrochemical Society. [DOI:10.1149/1.3258662] All rights reserved.