This study investigates the relationship between R&D expenses and profitability for a panel of U.S. firms in the energy sector. The analysis, spanning the period 1990–2011, differentiates the energy sector into two groups: firms that sell fossil energy sources to generate electricity and firms that sell renewable energy sources to generate electricity. The empirical findings show that R&D expenses have a stronger impact on profitability in the group of firms that sell renewable energy sources.