Traditional global powers like the European Union and the United States are seeing the rise of emerging powers like Brazil as prospective cooperation partners. Examining how traditional powers are perceived by their emerging counterparts offers critical insights into the prerequisites for effective and durable partnerships. While the literature on external perceptions has expanded considerably, a comparative perspective on how emerging powers perceive the policies of the two transatlantic powers in issue-specific areas is lacking. We present a framework of explanatory variables (legitimacy, coherence and negotiating style) and apply it to interview data and the literature to unravel Brazil's relations on biofuels with the EU and US, including through trilateral partnerships with third countries. Our data show that while Brazil's partnership with the US has progressed, the one with the EU has struggled to advance. Our paper seeks to explain these differences using our framework, advance understanding on the external perceptions of the international role and collaborative posture of the EU and US, and provide policy insights for the fruitful conduct of partnerships.