Abstract : In this paper we would like to determine whether the per capita real incomes of GCC countries are trend or difference stationary. The distinction is crucial for at least three reasons: one pertains to forecasting; while a trend stationary series tends to return to its long impact of such a shock forever. The second point is about econometric implications of the distinction as even minor divergences from difference stationarity would lead to non-robust cointegration estimations. The third point is about economics theory and policy; the distinction between the neoclassical and endogenous growth models can be setteled via empirical determination of the data to be difference or trend stationary. As the GCC countries strive to have more economic integration, correct identification of the issue becomes vital in policy making. After conducting a set of tests, we find that there is overwhelming evidence that the per capita real GDP of GCC countries is difference stationary.