As filed with the Securities and Exchange Commission on April 28, 2015May 30, 2017

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 20-F

ANNUAL REPORT PURSUANT TO

SECTION 13 OR 15(d) OF

THE SECURITIES EXCHANGE ACT OF 1934

For the fiscal year ended December 31, 20142016

Commission file number: 001-34175

ECOPETROL S.A.

(Exact name of Registrant as specified in its charter)

N/A

(Translation of Registrant’s name into English)

REPUBLIC OF COLOMBIA

(Jurisdiction of incorporation or organization)

Carrera 13 No. 36 – 24

BOGOTA – COLOMBIA

(Address of principal executive offices)

Tel. (571) 234 4000

Claudia Trujillo

Andrés Felipe Sánchez

Investor Relations Officer

investors@ecopetrol.com.co

Tel. (571) 234 5190

Carrera 13 N.36-24 Piso 75

Bogota, Colombia

(Name, Telephone, E-Mail and/or Facsimile number and Address of Company Contact Person)

Securities registered or to be registered pursuant to Section 12(b) of the Act.

Securities registered or to be registered pursuant to Section 12(g) of the Act: None

Securities for which there is a reporting obligation pursuant to Section 15(d) of the Act: None

Indicate the number of outstanding shares of each of the issuer’s classes of capital or common stock as of the close of the period covered by the annual report.

41,116,698,45641,116,694,690 Ecopetrol common shares, par value Ps$250COP$609 per share

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act.

x Yes¨ No

If this report is an annual or transition report, indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934.

¨ Yesx No

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.

x Yes¨ No

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files).

N/A

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, or a non-accelerated filer. See definition of “accelerated filer and large accelerated filer” in Rule 12b-2 of the Exchange Act. (Check one):

��

If an emerging growth company that prepares its financial statements in accordance with U.S. GAAP, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards† provided pursuant to Section 13(a) of the Exchange Act. ☐

† The term “new or revised financial accounting standard” refers to any update issued by the Financial Accounting Standards Board to its Accounting Standards Codification after April 5, 2012.

Indicate by check mark which basis of accounting the registrant has used to prepare the financial statements included in this filing:

If “Other” has been checked in response to the previous question, indicate by check mark which financial statement item the registrant has elected to follow:

¨ Item 17x¨ Item 18

If this is an annual report, indicate by check mark whether the registrant is a shell company (as
(as defined in Rule 12b-2 of the Exchange Act).

¨ Yesx No

Annual Report on Form 20-F 20142016

We file our Annual Report on Form 20-F and other information with the U.S. Securities and Exchange Commission.

We file reports, including annual reports on Form 20-F, and other information with the SEC pursuant to the rules and regulations of the SEC that apply to foreign private issuers. You may read and copy any materials filed with the SEC in the SEC’s public reference room at 100 F Street, NE, Washington, D.C. 20549. Please call the SEC at 1-800-SEC-0330 for further information on the operation of the public reference room. Any filings we make are also available to the public over the Internet at the SEC’s website at www.sec.gov and at our website at www.ecopetrol.com.co. (This URL is intended to be an inactive textual reference only. It is not intended to be an active hyperlink to our website. The information on our website, which might be accessible through a hyperlink resulting from this URL, is not and shall not be deemed to be incorporated into this annual report.)

Unless the context otherwise requires, the terms “Ecopetrol,” “we,” “us,”“Ecopetrol”, “we”, “us”, “our” or the “Company” are used in this annual report to refer to Ecopetrol S.A. and its subsidiaries on a consolidated basis.

References to the Nation in this annual report relate to the Republic of Colombia (“Colombia”), our controlling shareholder. References made to the Government of ColombiaColombian government or the Government correspond to the executive branch including the President of Colombia, the ministries and other governmental agencies responsible for regulating our business.

This annual report on Form 20-F contains forward-looking statements within the meaning of the safe harbor provisions of the U.S. Private Securities Litigation Reform Act of 1995. These statements are not based on historical facts and reflect our expectations for future events and results. Most facts are uncertain because of their nature. Words such as “anticipate,” “believe,” “could,” “estimate,” “expect,” “should,” “plan,” “potential,” “predicts,” “prognosticate,” “project,” “target,”“anticipate”, “believe”, “could”, “estimate”, “expect”, “should”, “plan”, “potential”, “predicts”, “prognosticate”, “project”, “target”, “achieve” and “intend,”“intend”, among other similar expressions, are understood as forward-looking statements. We have made forward-looking statements that address, among other things:

Our forward-looking statements are not guarantees of future performance and are subject to assumptions that may prove incorrect and to risks and uncertainties that are difficult to predict. Actual results could differ materially from those expressed or forecast in any forward-looking statements as a result of a variety of factors. These factors may include, but are not limited to, the following:

All forward-looking statements attributed to us are qualified in their entirety by this cautionary statement. We undertake no obligation to publicly update or revise any forward-looking statements, whether as a result of new information or for any other reason. Accordingly, readers should not place undue reliance on the forward-looking statements contained in this annual report.

The following table sets forth, for the periods and at the dates indicated, our selected historical financial and certain key operating data. The selected financial data has been derived from and should be read in conjunction with, and is qualified in its entirety by reference to, our consolidated audited financial statements, presented in Colombian Pesos. PricewaterhouseCoopers Ltda. audited our consolidated financial statements for the years ended December 31, 2014 and 2013. KPMG Ltda. audited our consolidated financial statements for the years ended December 31, 2012 and 2011. PricewaterhouseCoopers Ltda. also audited our consolidated financial statements for the year ended December 31, 2010.

Table 1 – Selected Operating Data

Financial Information

International Financial Reporting Standards (“IFRS”)

(Expressed in millions of Colombian Pesos, except for the net income per share and net operating income per share, which are expressed in Colombian Pesos)

Table 2 – Selected Financial Data

Our consolidated financial statements have beenfor the years ended December 31, 2014, 2015 and 2016 were prepared under the Public Accounting Regime (Régimen de Contabilidad Pública), or RCP,in accordance with IFRS as adoptedissued by IASB. References in this annual report to IFRS mean IFRS as issued by the Colombian National Accounting Office (Contaduría General de la Nación), or CGN in September, 2007 and applicableIASB. Our date of transition to Ecopetrol beginning withIFRS was January 1, 2014. Our consolidated financial statements for the fiscal year ended December 31, 2008. See Note 1—Economic Entity2015 were our first set of consolidated financial statements prepared in accordance with IFRS.

IFRS differs in certain significant aspects from the current reporting standards as in effect in Colombia (“Colombian IFRS”)), which is the accounting standard we use for local reporting purposes. As a result, our financial information presented under IFRS is not directly comparable to our financial information presented under Colombian IFRS. For a description of the differences between Colombian IFRS and Principal AccountingIFRS see sectionFinancial Review—Summary of Differences between Internal Reporting Policies and PracticesIFRS,.

Our consolidated financial statements were consolidated line by line and all transactions and balances between subsidiaries have been eliminated. These financial statements include the financial results of all subsidiary companies controlled, directly or indirectly, by Ecopetrol S.A. See Exhibit 1 – Consolidated companies, associates and joint ventures, to theour consolidated financial statements included in this Annual Report.annual report.

As indicated in paragraphs 9 and 18 of the International Accounting Standard 27 “Consolidated and Separated Financial Statements” we must present our financial information on a consolidated basis as if we were a single entity, combining the financial statements of Ecopetrol S.A. and its subsidiaries line by line, adding assets, liabilities, shareholder’s equity, revenues and expenses of similar nature, removing the reciprocal items among members of the Ecopetrol Group and recognizing non-controlling interest.  We referpresent our operating information on a consolidated basis.

The regulations of the SEC do not require foreign private issuers that prepare their financial statements on the basis of IFRS to RCP as Colombian Government Entityreconcile such financial statements to U.S. GAAP. Accordingly, while we have in the past reconciled our consolidated financial statements prepared in accordance with Colombian Government Entity GAAP differsto U.S. GAAP, those reconciliations are no longer presented in certain significant respects from generally accepted accounting principles inour filings before the United States, orSEC. We do continue to provide the disclosure required under the U.S. GAAP. Note 33Financial Accounting Standards Board (FASB) Accounting Standards Codification (ASC) Topic 932 “Extractive Activities—Oil and Gas” (which we refer to the consolidated financial statements included inas ASC Topic 932), as this Annual Report provides a descriptionis required regardless of the principal differences betweenbasis of accounting on which we prepare our financial statements. Other than as required under ASC Topic 932, any references to accounting treatments under Colombian Government Entity GAAP andor U.S. GAAP as they relate solely to the application of Colombian Government Entity GAAP or U.S. GAAP to our auditedhistorical consolidated financial statements and provides a reconciliation of net income and shareholders’ equity for the years and as of the dates indicated therein. As a state-owned company, our consolidated financial statements are periodically reviewed by the CGN. However, the review of our accounts by the CGN does not constitute an audit.statements.

In this annual report, references to “US$” or “U.S. dollars” are to United States dollars and references to “Ps$“COP$,” “Peso”“Colombian Peso” or “Pesos”“Colombian Pesos” are to Colombian Pesos, the Ecopetrol Group’s functional and presentation currency under which we prepare our consolidated financial statements. This annual report translates certain Colombian Peso amounts into U.S. dollars at specified rates solely for the convenience of the reader. Unless otherwise indicated, such Colombian Peso amounts have been translated at the rate of Ps$2,392.46COP$3,053.42 per US$1.00, which corresponds to theTasa Representativa Promedio del Mercado(TRM), or Average Representative Market Exchange Rate, for December 31, 2014.2016. Such conversion should not be construed as a representation that the Colombian Peso amounts correspond to, or have been or could be converted into, U.S. dollars at that rate or any other rate. On April 28, 2015,May 26, 2017, the Representative Market Exchange Rate was Ps$2,419.81COP$2,911.66 per US$1.00.

Certain figures shown in this annual report have been subject to rounding adjustments and, accordingly, certain totals may therefore not precisely equal the sum of the numbers presented. In this annual report a billion is equal to one with nine zeros.

In the second half of 2014, internationalDue to market imbalances, there was a sharp contraction in crude oil benchmarkprice, particularly in the first quarter of 2016. As demand proved to sustain itself while producers implemented previously announced capital expenditure reduction decisions that encompassed the adjustments necessary under the new price environment, the market began its path towards tighter balances (see Graph 1 – Supply/Demand vs ICE Brent price evolution). Although oil prices declined dramatically. From its peak in June 2014,have recovered from the Brent monthly contract price fell by more than 50% by year-end, directly impactinglowest prices during the revenueoil crisis, high levels of oil producing companies. It is believed that the main reason behind the drop in prices is an imbalance between global supply and demand. According to some estimates, 2014 global oil demand growth was 1,500 mboepduncertainty persist indicating a less than supply growth. Non-OPEC supply grew 2,090 mboepdsmooth recovery. Nonetheless, the change in 2014 with mostOPEC’s stance, announced at the end of September 2016 and later ratified in early December 2016, towards coordinated production cuts provided a lift that allowed the growth coming fromICE Brent price to end the United States (+1,590 mboepd). Thanks to the shale revolution, for the past three years, the United States has been the world’s fastest-growing hydrocarbon producer. U.S. crude oil production rose by 40% over that period, while natural gas production has grown by 29% since 2008, transforming this country into the main supplier of natural gas and the third largest supplier of crude oil worldwide. On the other hand, global demand grew 0.890 mboepd, mainly due to weak global economic growth of the Euro zone and Japan, along with lower expectations for China´s growth.year above US$55 per barrel.

Graph 1 – Supply/Demand Balance vs ICE Brent Price Evolution

Source: Energy Information Administration (EIA), “Annual Energy Outlook”.

PIRA Energy Group, “WorldWorld Oil Market Forecast”

Forecast (February 28, 2017)

Those imbalances caused a significant rise in global oil inventories during the first half of 2014, from 739 to 776 million barrels. As of December 31, 2014 global inventories were an estimated 770 million barrels, and since then they have increased further to 858 million barrels as of March 31, 2015. Historically such an excess of supply would have been offset through a cut in production from OPEC states. Nevertheless, OPEC members at their November 27, 2014 meeting decided to maintain their production levels. Given the fact that both the supply and demand of oil are relatively inelastic, particularly in the short term, Ecopetrol believes it will take some time for end consumers to see a reduction in gasoline prices significant enough to stimulate demand and for higher-cost production to decrease in reaction to lower crude prices. Thus, overall business sentiment points to an environment of short term weakness in crude oil prices.

Although international oil prices and global demand and supply dynamics are significant factors affecting our business and financial condition, Colombia’s local economic dynamics in Colombiafactors have also influenced and could continue to influence our performance given that we conduct substantially allmost of our business in Colombia. In 2014

The performance of Colombia’s gross domestic product (GDP) is one of the main drivers of fuel consumption in Colombia. According to the National Administrative Department of Statistics (DANE for its acronym in Spanish), during 2016 Colombia’s GDP grew by 4.6%,2% in real terms, as compared to 4.9%2015. The industries with the greatest growth rates were financial institutions, insurance, real estate and business services, construction and manufacturing. On the other hand, the industry with the largest drop in 2013, driven mainly by the performancegrowth was mining. Local sales of the construction, services and financial sectors. This economic performance resulted in higher local demand for liquid fuels which(diesel, gasoline, jet fuel and LPG) increased by 3.5%.2% mainly due to the increase in sales of gasoline. Gasoline domestic sales were more competitive than its substitutes due to its price decrease and fewer than expected conversions to natural gas for vehicles (NGV) in Colombia.

Recently,In 2016, there were no major changes in natural gas regulation. With respect to natural gas supply, in November 2016, a new regasification plant located in Cartagena became available, meaning that Colombia is now connected to the Colombian Government reduced its forecasted economic growthinternational LNG market and LNG prices will be a reference for 2015 from 4%-4.5% to 3.5%-4%, reflecting the impact of lower commodity prices, especially crude oilnational gas prices. Growth in 2015 is expected to be driven by the building construction and infrastructure sectors, mainly as a result of two ongoing programs: 4G (Cuarta Generacion) highway concessions, an ambitious program to build and operate under concession contracts more than 8,000 km of roads and 159 tunnels, and Mi Casa, a housing subsidy program aimed at Colombia’s low-income population that seeks to deliver 100,000 new houses at no cost plus other initiatives based on a reduction of the mortgage interest rate and direct subsidies.

The low oil price environment present at the end of 2015 and the beginning of 2016 led to a revision of our business plan 2015-2020, originally launched in May 2015, with a price scenario of US$80 per barrel. Our new 2017-2020 business plan is focused on value generation, profitability and financial sustainability under a price scenario of US$50 per barrel, and allows for considerable upsides in case of potential price increases. For example, if prices were to increase to an average price of US$70 per barrel, production by 2020 could reach 830 thousand barrels equivalent per day, or 16% over the current production.

The three pillars of the plan are: (i) cash flow focus and cost efficiency, (ii) strict capital discipline and (iii) profitable reserves and production growth.

Cash flow focus and cost efficiency: In 2015, we launched the 2015-2020 Transformation Program (the “Transformation Program”) with a goal of increasing our efficiency and decreasing cost. The Transformation Program has allowed us to decrease structural costs by US$1.5 billion compared to 2014. Such reduction has been accomplished due to the implementation of initiatives through our different business segments and corporate areas. The new business plan entails a second phase of the Transformation Program, with activities aimed to achieve excellence in project planning and execution as well as in our production, transportation, refining and marketing operations.

Capital discipline: We have preserved a rigorous level of capital discipline through the adjustment of investments and the adoption of strict controls to ensure that projects are delivered efficiently and within the expected time frame and budget. The plan calls for investments of approximately US$13 billion between 2017 and 2020. By 2020, approximately 90% of this investment will be allocated to the development of exploration and production projects, while investments in transportation and refining will seek to improve operational integrity and reliability.

As part of capital discipline, Ecopetrol is currently engaged in the approval phasedivestment of its strategy fornon-strategic assets and the period 2015-2030. This new strategy aims at generating sustainable value for Ecopetrol, reaffirming the Group’s strength aftersale of minor fields, and has also defined a decade of consistent growth that led Ecopetrol to consolidate its positiondividend policy as the largest Colombian company and one of the 35 largest oil companiesdescribed in the world.Section 6.2 Dividend Policy.

Ecopetrol has launchedProfitable growth in production and exploration: One of the pillars of the revised business plan is the view that a strong production portfolio and a greater exploratory success will bring about profitable growth. Under a price scenario of US$50 per barrel, production should average 760 thousand barrels of oil equivalent per day by 2020, an ambitious corporate transformation program in response to recent business dynamics and changesapproximately 6% growth from 2016. Approximately 94% of this production will come from the current producing assets.

In exploration, the plan estimates the incorporation of approximately 1,000 million barrels of contingent resources. In respect of adding reserves, we highlight the results of the exploratory campaigns in the global energy market, with two main objectives: (i) streamline processesColombian Caribbean offshore and improve the efficiencyGulf of the company to protect its financial and operational strength, and (ii) strengthen the capacities of Ecopetrol, to ensure a path for creating sustainable valueMexico in the medium and long term. In January 2015,United States. During the corporate transformation program was structured around eight key topics: Efficiency, Exploration, Recovery Factor, Culture and Leadership, Community Relationship, Projects, Technology and Capital Discipline.

Efficiency is the first axisperiod 2017 – 2020, Ecopetrol expects to add 600 million barrels of the transformation program. Ecopetrol is determined to achieve cumulative structural savings through the implementation of best practices in processes and focus on high-value activities. In addition, the program includes a thorough review of the project execution area and a more dynamic investment portfolio management, with the aim of optimizing capital allocation and ensuring that projects meet their budgets in terms of costs, time and profitability.

Strengthening the capacities of the company is also a key objective of the transformation program. For this reason, Ecopetrol is already structuring a comprehensive program for the improvement of its oil recovery factor, which will maximize cash generationproven reserves from current productive fields. In addition, Ecopetrol will reinforce its technical capabilities in explorationfields and will launch a capacity-building technology program, fundamental to the creation of sustainable value in the oil and gas industry. Finally, the transformation program aims at designing a new model for successfully relating Ecopetrol with its environment, and includes actions intended to reinforce the corporate culture of Ecopetrol and enhance its human talent and leadership.

This transformation program is the first piece of a new strategy for Ecopetrol for the period 2015-2030, which will be presented in detail once approved definitively by the Boardexploration.

Consistent with the new corporate strategybusiness plan update, in November 2016, the long term, and after a thorough reviewboard of the project portfolio to prioritize investments that maximize shareholder value, the directors of Ecopetrol (“Board of Directors of EcopetrolDirectors”) approved a $7.860US$3.5 billion investment plan for the year 2015.2017. The plan aims at achievingEcopetrol Group will continue to produce an annual average production of 760about 715 thousand barrels of oil and gas equivalent per day during 2017. This production level lays the foundation for the corporate group, of which 710 thousand correspond to Ecopetrol S.A.Ecopetrol’s expected increase in production by 2020.

OutMost of the total $7.86 billioninvestment will be in exploration and production. In refining, petrochemicals and biofuels, and transportation and logistics, investments will be made to comply with integrity and operational requirements as well as project completion. The table below sets forth the details of the investment plan approved for the Corporate group, $4.11 billion will be invested directly by Ecopetrol S.A. and $3.75 billion by subsidiaries, including $1.93 billion to be contributed by Ecopetrol S.A to its subsidiaries. Out of these investments, 92% will be held in Colombia and the remaining 8% abroad through subsidiaries. The highest percentage of resources will be directed toward production, the culmination of the modernization of the Cartagena refinery and the strengthening of the transportation capacity. The detail of the investments approved per segment is as follows:business segment.

Table 3 – 2017 Investment Plan