Two decades of research on the euro’s trade effects have produced estimates ranging from 4% to 30%. We find this divergence may reflect genuine hetero- geneity across country pairs rather than methodological differences. Using Eurostat data on 15 EU countries (1995–2015), we estimate euro adoption increased bilateral trade by 29% on average (14.1% after fixed effects correc- tion), with effects ranging from−12% to +79% across pairs. Core eurozone pairs show large gains while peripheral pairs involving Finland, Greece, and Portugal saw smaller or negative effects, some statistically significant. Pre- euro trade intensity and GDP account for over 90% of feature importance in explaining this heterogeneity. Extending to EU28, crisis-era adopters pull down naive estimates to 4.3%, but fixed effects correction recovers 13.4%, consistent with the EU15 baseline. Counterfactual analysis suggests varied effects for non-eurozone members: UK (+33%), Sweden (+22%), Denmark (+19%).