In the first part, discusses rationale for the prohibition of riba. In the second part, explains the reasons for the success of Islamic banks as: (i) efficient banking services; (ii) less risky advances; (iii) reasonably high returns on investment; and (iv) low risk of returns. Then discusses the results of an empirical study carried out for F.I.B Sudan. The study suggested that the profit-sharing ratio is the most sensitive variable. The banks should not change it. Instead they can adjust their investment portfolio mix as well as the range of banking services. Foreconomists and bankers. Based on primary sources. Does not contain the mathematical model referred to in the main text of the paper.