Venezuela has signed a key protocol that puts the oil-rich nation on track to become a permanent member of South America's main trade bloc, Mercosur.

Caracas and Mercosur's four member countries -- Argentina, Brazil, Uruguay and Paraguay -- signed the protocol late Tuesday.

The document sets a four-year timetable for full membership and gives Venezuela until 2012 to enforce common tariffs and respect free trade within the grouping. Some safeguards and extensions are allowed.

The four Mercosur presidents still have to ratify the deal during an upcoming summit.

Venezuelan President Hugo Chavez said Wednesday the protocol puts his country on the right political, social and economic track.

The signing came just weeks after Caracas withdrew from another South American grouping (the Andean Community of Nations) to protest bilateral trade deals between members Peru and Colombia and the United States.

Mercosur was formed in the 1990s by the South American nations of Brazil, Argentina, Uruguay and Paraguay to increase regional economic cooperation.

As an associate member, Venezuela currently is barred from participating in alliance tariff agreements.

Some information for this report was provided by Reuters.