Ecopetrol, formerly known as Empresa Colombiana de Petróleos S.A. (English: Colombian Petroleum Co. Not to be confused with the US owned and operated Colombian Petroleum Co. (COLPET) and sister company South American Gulf Oil Co. (SAGOC) dating to the 1930s which were taken over by the state owned Ecopetrol in the 1970s) is the largest and primary petroleum company in Colombia. As a result of its continuous growth, Ecopetrol forms part of the Fortune Global 500 and is ranked 303, it belongs to the group of the 25 largest petroleum companies in the world, and it is one of the four principal petroleum companies in Latin America.
Even though there were attempts as early as 1941 for the Colombian government to legally take over the Tropical Oil Co., it wasn't until the legal end of the contract of the Concesión De Mares expired that a transfer of ownership could take place. The reversion of "De Mares Concession" ("Concesión De Mares") to the Colombian State on 25 August 1951 gave way to the Empresa Colombiana de Petróleos, which had been created in 1948 by means of Law 165 of that same year. The growing company assumed the reverted assets of the Tropical Oil Co. that began oil activities in 1921 in Colombia with the implementation of the Cira-Infantas Field in the Middle Magdalena River Valley, located some 300 kilometers northeast of Bogotá. Ecopetrol undertook activities in the oil chain as a state-owned industrial and commercial company in charge of administrating the nations hydrocarbon resources, and grew as other concessions reverted and became part of its operation. The nationalization of Ecopetrol was not smooth and met with some opposition and skepticism as to how the company, if held nationally could in fact be able to keep up with the complex and expensive operations without outside expertise in the changing international market. A call for nationalization was nevertheless made.