The reversion of "The Mares Concession"  to the Colombian State on August 25, 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 Company 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 nation's hydrocarbon resources, and grew as other concessions reverted and became part of its operation.

In 1961, it assumed the direct management of the Barrancabermeja Refinery.  Thirteen years later, it purchased the Cartagena Refinery, built by Intercol in 1956.

In 1970, it adopted its first by-laws, which ratified its nature as a State-owned Commercial and Industrial Company, linked to the Ministry of Mines and Energy, fiscally supervised by the General Comptrollership of the Republic of Colombia.

In September 1983, the best news for the history of Ecopetrol and some of the best news for Colombia was given: the discovery of the Caño Limón Field in association with OXY, a reservoir with reserves estimated at 1.1 billion barrels.  Thanks to this field, the Company began a new era and in the year 1986, Colombia began to export oil again.

During the 1990s, Colombia extended its oil self-sufficiency with the discovery of the Cusiana and Cupiagua giants in the Foothills of the Plains region, in association with the British Petroleum Company.

In 2003, the Colombian government restructured the Empresa Colombiana de Petróleos, in order to internationalize it and make it more competitive in the framework of the world hydrocarbon industry.

Decree 1760 / June 26, 2003 (available only in spanish) modified the organic structure of the Empresa Colombiana de Petróleos and made it Ecopetrol S.A., a public stock-holding corporation, one hundred percent state-owned, associated with the Ministry of Mines and Energy, and governed by its by-laws contained in Notarized Document No. 2931 / July 7, 2003, issued by the Second Notary Public of the Bogotá D.C. Circle.

The transformation of the Empresa Colombiana de Petróleos into the new Ecopetrol S.A., released the Company from State functions as the administrator of the oil source and the ANH (Agencia Nacional de Hidrocarburos) [National Hydrocarbons Agency] was created to carry out the function.

As of 2003, Ecopetrol S.A. began an era in which, with more autonomy, it has accelerated its exploratory activities, its capacity to obtain results with a business and commercial vision and the interest in improving its competitiveness on the world oil market.