The negotiations for a new instrument for the conservation and sustainable use of high-seas marine biodiversity (marine biodiversity beyond national jurisdiction; BBNJ) finally concluded after difficult negotiations. The BBNJ negotiations had to address a regime complex of sectoral and regional organizations regulating different aspects of marine biodiversity and a political struggle about the epistemologies that ought to inform marine biodiversity governance, which is driven by limited, unequally distributed, and contested knowledge. However, to be implemented, the new BBNJ Agreement will have to be equipped with expert authority to be able to address these challenges and make competent statements about the state of high-seas marine biodiversity. We address a gap in empirical work on expert authority in the regime complex by analyzing state references to the expertise of different international organizations in the BBNJ negotiations. Combining collaborative event ethnography and social network analysis, we show that states strategically and politically refer to the expertise of international organizations, and we coin the term authority shopping to describe this behavior.