William Gervase (School of Oriental and African Studies, University of London, UK) Clarence-Smith 
The Economics of the Indian Ocean Slave Trade in the Nineteenth Century [PDF ebook] 

First Published in 1989. Well over a million slaves were exported from Indian Ocean and Red Sea ports in Eastern Africa during the nineteenth century, and millions more were shifted around the interior of the continent and along the coast of East Africa. And yet we still know remarkably little about this great movement of people, particularly from an economic point of view. This is a collection of twelve essays looking at the economics of the Indian Ocean and the Red Sea Slave trades of the nineteenth century.