Purpose: Effective tax rates can have dual effect in the economic policy of a country by maintaining the state revenues in sustainable levels providing a safe net for the economic development. If taxation struggles the economy, there should be a turning point were the results of high tax rates do not have the expected results on the state revenue. The parabolic relation of Laffer curve is tested on a data set of different OECD countries. Design/Approach/Methodology: Three different functions have been selected to test the Laffer curve starting from the fact that the relation of revenues with taxes should have a parabolic form, with the turning point to be the peak of the parabola. Findings: The findings suggest that there exists a peak point where taxation policy is not providing the expected revenues. Results suggest that this pattern is common in several countries with different taxation regimes. The effective tax rates are different between the countries. Countries are divided into clusters with the same effective tax rates. The relation of the tax revenue and taxation rates is adjusted with the tax moral of the country. Practical Implications: The results are compared with other possible forms of the relation of revenue and taxes with considerable importance.