Since the beginning of the 20th century, several hundred bilateral ATAs have been signed. The TREND project of the Canada Research Chair in International Political Economy lists approximately 700 trade agreements, the vast majority of which are bilateral.  A preferential trade area (also known as a preferential trade agreement, PTA) is a trading bloc that grants preferential access to certain products of participating countries. This is done by lowering tariffs, but not by abolishing them completely. A PTA can be set by a trade pact. This is the first step in economic integration. The boundary between a PTA and a free trade area (FTA) can become blurred, as almost all PTAs have the primary objective of becoming a free trade agreement under the General Agreement on Tariffs and Trade. These tariff preferences have led to numerous derogations from the principle of normal trade relations, namely that members of the World Trade Organization (WTO) should apply the same tariff to imports from other WTO members.  With the recent increase in bilateral PTNPs and the emergence of mega-PTNs (large regional trade agreements such as the Transatlantic Trade and Investment Partnership (TTIP) or the Trans-Pacific Partnership (TPP)), a global trading system managed exclusively within the framework of the WTO seems unrealistic and interactions between trading systems must be taken into account. The increasing complexity of the international trading system resulting from the proliferation of PTAs should be taken into account when considering the choice of forums used by countries or regions to promote their trade relations and environmental agenda.
 NTPs have grown rapidly; in the 1990s, there were just over 100 ENTPs. In 2014, there were more than 700.  In 2004, Scott Baier and Jeffrey Bergstrand published that there are three economic determinants that are essential to the formation of APPAs. Countries are more likely to participate in APTs if they have low transport costs and larger savings. Third, countries of similar economic size are likely to benefit most from APT training. Economic determinants such as GDP, similarity in economic size and distance between countries correctly predict more than 80% of the PTNs in force from 2020 on.  Table 3 Mercosur: Export growth by destination market, 1991/98 a Cumulative change 1991/98 Source: Official national figures Table 2 Mercosur: Geographical composition of trade, 1998 (in percentage and billions of trade). Table 4 Mercosur: Share of intraregional exports in GDP, 1991/98 The other CECs can be attributed to political predictors.