Economic determinants like GDP, similarity of economic size, and distance between countries correctly predict over 80% of PTAs in effect as of 2020. Third, countries with similar economic sizes are likely to benefit the most by forming PTAs. Countries are more likely to participate in PTAs if they have low transportation costs and larger economies. In 2004, Scott Baier and Jeffrey Bergstrand published that there were three economic determinants critical to the formation of PTAs. PTAs have seen rapid growth in the 1990s, there were slightly more than 100 PTAs. The increased complexity of the international trade system generated by the multiplication of PTAs should be taken into account in the study of the choice of fora used by countries or regions to promote their trade relations and environmental agenda. With the recent multiplication of bilateral PTAs and the emergence of Mega-PTAs (wide regional trade agreements such as the Transatlantic Trade and Investment Partnership (TTIP) or Trans Pacific Partnership (TPP)), a global trade system exclusively managed within the framework of the WTO now seems unrealistic and the interactions between trade systems have to be taken into account. These tariff preferences have created numerous departures from the normal trade relations principle, namely that World Trade Organization (WTO) members should apply the same tariff to imports from other WTO members. It is the first stage of economic integration. This is done by reducing tariffs but not by abolishing them completely.
A preferential trade area (also preferential trade agreement, PTA) is a trading bloc that gives preferential access to certain products from the participating countries.