The article focuses on the recent regional cooperation developments in the form of regional trade agreements (RTA) and on the influence of the RTA on the Multilateral trading system and on trade and economic unterests of the third parties (i.e. non-members of the relevant RTA) as well as on the world trade in general. The author analyses the tendency to broaden the range of issues covered by the newly negotiated RTA. Particular attention is paid to developing the new rules for regulating international trade and to the relationship between trade regulation at the regional and multilateral levels, with regard to the debate on ways to further development of existing multilateral mechanisms for regulating international trade. The article describes the creation by RTA of preconditions that may give the Multilateral trading system new features of somewhat hybrid nature. The paper provides discussion on how the regionalism affects the dispute settlement mechanism and on the applicability of multilateral dispute settlement rules for the purposes of resolution of trade disputes within the RTA. The author develops arguments in favor of vital necessity to ensure transparency in negotiation of new RTA as a crucial factor for maintaining integrity and efficiency of the multilateral framework for regulation of international trade and of a multilateral trading system in general.