Fossil fuel producers have a major role to play in curbing greenhouse gas emissions through supply-side initiatives. Yet, no study has systematically assessed the determinants of efforts to constrain fossil fuel production for climate purposes. To contribute to climate change mitigation efforts, this article develops a conceptual framework for factors potentially affecting country-level initiatives to keep fossil fuels in the ground. Using data for 124 countries with fossil fuel reserves for 2006–2019 and multivariate Poisson regression analysis, we identify factors influencing the use of such constraints by national governments. Results show that although dependence on fossil fuel rents reduces the likelihood of constraint measures, the size of fossil fuel reserves or production does not impact it. Richer countries are also more likely to use constraints. Organization of Petroleum Exporting Countries membership constitutes a barrier to having moratoria on fossil fuel extraction. These results can help identify potential members for new fossil fuel supply-side initiatives and coalitions.