This paper examines the realms of law, custom, and lineage that operated between Oman and East Africa in the late 19th and early 20th centuries. In the 1830s, the Omani sultan Said b. Sultan al-Busaidi relocated his capital to the African island of Zanzibar. When he died in 1856, a succession dispute simmered between his heirs. British intervention in 1861 resulted in a treaty dividing the empire, affirming separate al-Busaidi rulers in Arabia and Zanzibar. The 1861 Canning Award, like the earlier Anglo-Omani treaties to end the slave trade, established in British minds a legal basis for intervention. Between Muscat and Zanzibar, British officials policed high politics, and the British Navy patrolled the Indian Ocean sea lanes. Thus as Sugata Bose argues, British officials established a unitary sovereignty to replace the layered and shared sovereignty that had characterized the Indian Ocean of an earlier period. At the level of individuals, however, the formal division of Arabian and African dominions did not stem the flow of migrants from impoverished Oman to the wealthy Swahili Coast. Overlapping commercial, legal, and kin networks continued to link the regions. Some benefitted from these as kinsmen's wealth from Africa expanded settlements in Oman. The same mobility, however, brought into question the efficacy of law and tradition in Oman, as Arabs in Zanzibar manipulated property holdings and water rights in Arabia to their advantage. Using standard Islamic legal practices--mortgages, time sales, and complete sales--Omanis in East Africa secured loans and raised capital for ventures abroad. Those left behind in Oman found their access to family property preempted by mortgages and contracts drawn in East Africa without their consent. As Omanis in Zanzibar took refuge in legal norms enforced by mixed (Ibab, Sunni, and British) courts, those in Arabia invoked custom to defend their access to resources. The thesis of this paper is that even as British imperial designs tightened controls to limit rulers in both Oman and Zanzibar, the mobility of individuals set against the heterodox legal possibilities of the Indian Ocean allowed new negotiations over land, law, and custom. This paper draws on two methodologies: analysis of archival materials and interpreting interviews. The sources include contracts, letters, and legal cases in Arabic and English from the Zanzibar Archives; documents from India Office Records in London; and interviews and family histories collected by the author in Oman, Tanzania, and Burundi.