Anglo-American whalemen in the eighteenth and nineteenth centuries used customs largely of their own creation to resolve disputes at sea over contested whales. These customs were remarkably effective as litigation was rare and violence even rarer. Legal scholars such as Robert Ellickson have correctly pointed to these customs as an example of how close knit communities settle disputes without recourse to formal legal institutions or even knowledge of the applicable law. Ellickson’s belief, however, that these whaling customs were universally followed at sea and were – in turn – adopted by courts, is not entirely accurate. While courts often deferred, in part, to whaling practices, judges and lawyers were also active participants in creating the property law of whaling. British courts at the turn of the nineteenth century did much to advance one whaling custom over a competing practice. In the 1820s, British lawyers and judges applied the emerging action of interference with trade to whaling disputes and thereby reintroduced aspects of the custom their predecessors had previously rejected.