There is growing interest in carbon-free electricity procurement by electric companies, large electricity customers, and other stakeholders, including procuring and supplying carbon-free energy 24 hours per day, 7 days per week (24/7 CFE). This analysis uses EPRI’s U.S. Regional Economy, Greenhouse Gas, and Energy Model (US-REGEN) model to assess potential system effects of voluntary CFE procurement across a range of assumptions about program design, participation, and eligible technologies as well as regional variation in these impacts. Model results suggest that annual (volumetric) matching has more limited effects on system emissions than hourly matching—13-38% of carbon reductions. The combination of hourly temporal matching, use of new resources, and local deliverability can maximize emissions reductions from CFE procurement but at a cost premium that varies by region, participation level, and technology availability. The definition of qualifying CFE resources alters technology strategy and costs, and broader portfolios of generation, energy storage, and carbon removal options lower costs, especially in regions with lower wind and solar resource quality.