Panel data methodology is used to estimate equations (3a-b). We mainly apply Feasible Generalized Least Squares (FGLS) combined with the Seemingly Unrelated Regression (SUR) technique, thus controlling for correlation between error terms over time and between cross-sections. The use of panel data methodology has several advantages over cross-section analysis. First, panels make it possible to capture the relevant relationships among variables over time. Second, a major advantage of using panel data is the ability to monitor the possible unobservable trading-partner pairs’ individual effects. When individual effects are omitted, OLS estimates will be biased if individual effects are correlated with the regressors. Mátyás (1997), Chen and Wall (1999) and Egger (2000) present a discussion of the advantages of using this methodology to estimate the gravity equation of trade. Panel unit-root tests are conducted for exports in real terms (aggregated), the real exchange rate, total income, per capita income differences and transport costs. Stochastic trends that express themselves as autocorrelation of the error terms are found to prevail in all series analysed. Due to missing data and possibly an insufficient number of observations, Period SUR15 cannot be performed. We control for autocorrelation of the disturbances by plugging in AR-terms whenever they prove to be significant. Simulations are based on 1988-2002 data and the coefficients for this period.