Rent clearly has a bad reputation. Beyond the simple matter of economic efficiency, the concept has carried since the beginning of the 19th century negative moral connotations, which seem to have affected the general perception of rentier states. Conscious of these negative biases, analysts worked to correct the approximations and generalizations of the first models. Rentier economies suffer from an important weakness related to the exogenous nature of their principal revenue. Exporting countries have little control over the fluctuations in the globalized energy market, and the interdependence between producers and clients is one of the market’s major characteristics. The recipients of rent were therefore never immune to possible crises and their conduct progressively incorporated this vulnerability. In addition, rentier states are clearly conscious that exploitation of resources will eventually lead to their running out and they therefore have to prepare for this post-rent phase. The rentier debate has for a long time focused mainly on the question of how revenue is used, but it has now more to do with the question of good management or simply management under socio- political constraint. The economic analysis of the rent initially more or less ignored taxation issues and did not dwell on the development of local financial systems. Yet even if rent is not sustainable in itself, it can become so if it is invested in a way that generates new sources of revenue. It then becomes interesting to try and assess how oil and gas revenues have been used since the first oil-shock. Have rentier gulf countries reached a sustainable growth model? Have they invested enough to achieve diversification of their respective economies