Hourly matching of green hydrogen against renewable energy purchases, starting in 2028 under the U.S. Treasury’s draft guidelines for Section 45V of the U.S. Inflation Reduction Act, might make converting current gray hydrogen users—especially, petroleum refiners—out of reach. Unless early projects are grandfathered for annual matching, other sectors such as manufacturing, eFuels and utility deployment will likely lead the way in near-term adoption of green hydrogen.