 Katouzian has written extensively in pure and applied economics, but his original contributions in economics are in the theory of the development of the service sector, the economics of petroleum-exporting countries, and economic method and philosophy.As early as the late 1960s he predicted that the share of services in output and employment would rapidly grow in advanced countries and in some developing countries, for different sets of reasons, and that the share of non-factor services in international trade would also grow steadily, the advanced countries tending to specialize in the export of services.Also, he was one of the first economists, from the late 1960s, to describe petroleum revenues received by the petroleum-exporting countries as economic rent, and the countries in question as rentier economies, and studied the effect of the receipt of the petroleum rent by the state on the economics as well as politics of petroleum-exporting countries.