The use of hydrogen addition to the natural gas feedstocks of midsize (30-150MW) gas turbines was analyzed as a method of reducing nitrogen oxides (NOx). The costs of hydro-en addition as a function of its ability to reduce NO., were investigated. Hydrogen addition was evaluated against Current control technologies for both existing and new systems to determine its benefits and market feasibility. Markets for NOx, emissions credits currently exist in California and the Northeast States and are expected to grow; therefore, potential sale of emissions credits for volunteer retrofits was also included in this study. (c) 2005 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.