Score contribution per author:
α: calibrated so average coauthorship-adjusted count equals average raw count
•UCO imports rose 750 % since 2022, now supplying 35 % of U.S. bio-based diesel inputs.•Imported UCO displaces traceable U.S. crop oils under carbon intensity scoring rules.•Lax certification standards enable fraud and undermine policy climate credibility.•CI recalibration, audit systems, and targeted incentives can support U.S. feedstocks.•Balanced reforms can sustain trade while improving environmental and market outcomes.