Exhibit 4.13



| | Addendum N° 6Framework Crude Services Agreement | 
| | ----------------------------------------------- | 
|












Addendum
No. 6

Framework Crude Services Agreement










Between



CENIT
Transporte y Logística de Hidrocarburos S.A.S.



and



ECOPETROL
S.A.



Bogotá
D.C., April 25, 2016










| | Addendum N° 6Framework Crude Services Agreement | 
| | ----------------------------------------------- | 
|



Addendum
No. 6 to the

Framework
Crude Services Agreement



This Addendum (“Addendum No. 6”)
to the Framework Crude Services Agreement (the “Agreement”) is entered into on this day, April twenty-fifth
(25th), 2016 (hereinafter the “Signing Date”), by the following parties (hereinafter the “Parties”,
and each of them a “Party” or the “Party”):





| | 1. | CENIT TRANSPORTE Y LOGÍSTICA DE HIDROCARBUROS
S.A.S., a Colombian simplified stock corporation [sociedad por acciones simplificadas] organized pursuant to a private
document dated June fifteenth (15th), 2012, registered with the commercial registry on June fifteenth (15th), 2012, with commercial
registration No. 02224959 (hereinafter “CENIT”), represented for the signing of this Addendum by THOMAS
RUEDA EHRHARDT, acting in his capacity as legal representative of CENIT; and
| | -- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



| | 2. | ECOPETROL S.A., a Colombian mixed privately/publicly owned corporation [sociedad de
                                                                                                                           economía mixta], associated with the Ministry of Mining and Energy, authorized by Law 1118 of 2006, acting in
                                                                                                                           accordance with its bylaws and having principal domicile at Bogotá, D.C., with NIT 899.999.068-1, represented for the
                                                                                                                           signing of this instrument by JUAN CARLOS ECHEVERRY GARZÓN, identified as shown beneath his signature, who is
                                                                                                                           acting in his capacity as Chief Executive Officer, authorized to enter into this addendum in accordance with the provisions of the
                                                                                                                           ECOPETROL S.A. Bylaws (hereinafter “ECOPETROL”), and
| | -- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------





The Parties have approved the aspects set forth
below, subject to the following



RECITALS



| | 1. | On
                                         April 1st, 2013, CENIT and ECOPETROL entered into the Framework Agreement
                                         for complete provision of the Services (as defined in the Agreement), pursuant to which
                                         CENIT provides to ECOPETROL Crude Transport Services by Pipeline along the Galán
                                         – Ayacucho Corridor.
| | -- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



| | 2. | The reduction in ECOPETROL’s production of light and medium crude, as well as the trend among
domestic producers (third parties) to export all their production, has rendered difficult the process of purchasing appropriate
crude (raw material) for the Barrancabermeja Refinery in the domestic market. In that regard, it has been noted that the medium
and light crude content in the refinery’s diet has declined, which has affected its operations by forcing it to reduce its
load in order to operate with a diet of increasingly heavy crude. In studying the transport systems to which the Barrancabermeja
Refinery is connected, it was determined that it is possible to mitigate this problem by increasing the availability of light and
medium crudes transported along the Caño Limón – Coveñas Oil Pipeline (eastern corridor), since mixes
of heavy crude are being transported along the western corridor.
| | -- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



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| | Addendum N° 6Framework Crude Services Agreement | 
| | ----------------------------------------------- | 
|



| | 3. | To be able to supply appropriate crude (light/medium) to the Barrancabermeja Refinery, ECOPETROL
asked CENIT to amend the Framework Services Agreement, to guarantee that the 14” Galán – Ayacucho line can also
transport an average minimum of thirty thousand barrels per calendar day (30,000 bpcd) in the direction Ayacucho – Galán
under the Quality Specifications set forth in Annex TC-1 of the Agreement for Vaconia Blend or Caño Limón Crude (hereinafter
the “Reversal Plan”).
| | -- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



| | 4. | To address ECOPETROL’s needs, the entry into operation of the Reversal Plan implies that
CENIT must undertake a series of investments and operational adjustments, to which end the Parties agree that this Addendum No.
6 will establish the terms and conditions by which ECOPETROL will adequately compensate CENIT for the aforementioned investments
and adjustments.
| | -- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------





Pursuant to the above recitals, CENIT and ECOPETROL



AGREE:



ONE.-As compensation for the necessary
investments and operational adjustments required for the entry into operation of the Reversal Plan, the Parties agree the payment
of the following monetary considerations, in accordance with the terms set forth below:



“Monetary considerations,
Reversal Plan:



Notwithstanding monthly payment
of the Fee for provision of Services on the 14” Galán – Ayacucho Oil Pipeline to which CENIT is entitled, as
set forth in Section 5.02 of the Agreement, the investments and operational adjustments shall be recovered through monthly payment
by ECOPETROL, where applicable, of the following monetary considerations, over a period of seven (7) Calendar Years counting from
the Effective Date of this Addendum No. 6 (hereinafter the “Term for the Monetary considerations of the Reversal Plan”):



| | (i) | A fixed monetary consideration equivalent to FORTY-NINE THOUSAND, TWO HUNDRED SEVENTY-FIVE US
dollars (USD$ 49,275), as compensation for the investments made to place the Reversal Plan into operation, resulting from the product
of multiplying thirty thousand Barrels per Calendar Day (30,000 BPCD) by ZERO POINT ZERO FIVE FOUR US DOLLARS (USD$ 0.054) for
three hundred sixty-five (365) Days, divided by twelve (12) Calendar Months during the Term of the Monetary Considerations of the
Reversal Plan (hereinafter the “Monetary Consideration for Investment”); plus
| | --- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



| | (ii) | A fixed monetary consideration for ECOPETROL’s use of the 14” two-way Galán
– Ayacucho line in the direction Ayacucho – Galán on one Day of the Month of Operations invoiced, which will
apply regardless of the volume effectively transported by ECOPETROL (hereinafter the “Fixed Monetary Consideration for
Use of Reversal”). The monthly value of the Fixed Monetary Consideration for Use of Reversal shall result from the product
of multiplying thirty thousand Barrels perCalendar Day (30,000 BPCD) by ZERO POINT EIGHT ZERO SEVEN US DOLLARS (USD$ 0.8070) for each Day ECOPETROL
effectively uses the 14” two-way Galán – Ayacucho pipeline in the direction Ayacucho – Galán during
a Month of Operations; plus
| | ---- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



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| | Addendum N° 6Framework Crude Services Agreement | 
| | ----------------------------------------------- | 
|



| | (iii) | A variable monetary consideration applicable as of Barrel number thirty thousand one (30,001)
effectively carried on the 14” two-way Galán – Ayacucho pipeline in direction Ayacucho – Galán
on one Day of the Month of Operations invoiced (hereinafter the “Variable Monetary Consideration for Use of Reversal”).
The monthly amount of the Variable Monetary Consideration for Use of Reversal shall result from the product of multiplying ZERO
POINT EIGHT ZERO SEVEN US DOLLARS (USD$ 0.8070) by each additional Barrel over thirty thousand Barrels per Calendar Day (30,000
BPCD) effectively carried on one Day of the Month of Operations.
| | ----- | -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



The Fixed Monetary Consideration for Use
of Reversal and the Variable Monetary Consideration for Use of Reversal shall not apply and therefore may not be invoiced by CENIT
for Days when the 14” two-way Galán – Ayacucho pipeline operates in direction Galán – Ayacucho,
provided that on that same Day the 14” two-way Galán – Ayacucho pipeline has not operated in direction Ayacucho
– Galán.”



TWO.-As of the Effective Date, the
Galán – Ayacucho Corridor identified in Annex TC-7 of the Crude Transport Service by Oil Pipeline – Contracted
Capacity of ECOPETROL for each Oil Pipeline, shall be understood as being included in the 18” Galán – Ayacucho
and the 14” two-way Galán – Ayacucho pipelines.



THREE.-To amend, as of the Effective
Date (as this term is defined in Clause 4 of this Addendum No. 6), Annex TC-8 of the Crude Transport Service by Oil Pipeline –
Oil Pipelines Entry and Exit, to include the new entry points for the 14” two-way Galán – Ayacucho line in direction
Ayacucho – Galán, which shall read as follows:



|System(Line)                              | InitialStation                                                                                                                                                                                      | EndStation                                                                                                                                                                                          | Initial Custody TransferPoint                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              | Final Custody TransferPoint                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|----------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|14” Two Way Ayacucho – Galán
        Line | (Direction Ayacucho – Galán)
        
        
        Ayacucho
        
        
        
        
        
        
        
        (Direction Galán – Ayacucho)
        
        
        Galán | (Direction Ayacucho – Galán)
        
        
        Galán
        
        
        
        
        
        
        
        (Direction Galán – Ayacucho)
        
        
        Ayacucho | (Direction Ayacucho – Galán)
        ŸOfficial Measurement: Dynamic and/or Static from Ayacucho
        ŸTransfer point: ACN metering system at Ayacucho and dedicated tanks.
        ŸPhysical limit of border or pumping facility [bateria]: closest link [brida] to the Ayacucho metering system.
        Closest link to the valves of the Ayacucho
        storage tanks
        
        
        (Direction Galán – Ayacucho)
        ŸOfficial Measurement: Static
        Pump House 8 Ÿ
        Transfer point: at the tanks of Pump House 8
        ŸPhysical limit of border or pumping facility: closest link to the valves of the Pump House 8 storage tanks | (Direction Ayacucho – Galán)
        ŸOfficial measurement: Dynamic Pump House 8
        Ÿ Transfer point: at the meters
        ŸPhysical limit of border or pumping facility: at the link of the downstream connection of the Pump House 8 meters.
        
        
        
        
        
        (Direction Galán – Ayacucho)
        ŸDynamic measurement from Ayacucho at meters 1301 and 1302
        ŸTransfer point at the Ayacucho dynamic meters
        ŸPhysical limit of border or pumping facility: closest link to the Ayacucho metering system.



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| | Addendum N° 6Framework Crude Services Agreement | 
| | ----------------------------------------------- | 
|



FOUR.-The Parties shall understand
by Effective Date of Addendum No. 6 the date that CENIT indicates to ECOPETROL as the Day the Reversal Plan is operationally available,
provided that all necessary permits and authorizations have been obtained for its entry into operation.



In any event, the notification must be made
a minimum of sixty (60) Days in advance of the first Day of the Month of Operations of the direction Ayacucho – Galán
of the 14” two-way Galán Ayacucho pipeline.



CENIT may amend the date of notification mentioned
in this clause, notifying ECOPETROL in writing again of the date when the Reversal Plan will be operationally available, prior
to the date initially indicated, without thereby implying any responsibility or breach whatsoever by CENIT. Consequently, the Parties
shall understand that the Effective Date shall be the date set forth in the aforementioned communication.



FIVE.-ECOPETROL may not exercise the
rights assumed in Part (ii) of Section 3.05 of the General Conditions of the Agreement upon final release of Firm Capacity in the
Galán Ayacucho Corridor during the Term of the Monetary Consideration for the Reversal Plan. In any event, the Term of the
Monetary Consideration for the Reversal Plan shall not suspend the term set forth in Section 3.05 (ii) (c) of the Agreement.



SIX.-The Parties agree that the Monetary
Consideration for Investment, the Fixed Monetary Consideration for Use of Reversal and the Variable Monetary Consideration for
Use of Reversal as described in Clause One of this Addendum No. 6 shall not be subject to any adjustment or indexation over time.



SEVEN.- Without prejudice to the provisions
of Clause One of this Addendum No. 6, the Fixed Monetary Consideration for Use of Reversal and the Variable Monetary Consideration
for Use of Reversal may be subject to revision by CENIT in the event that ECOPETROL undertakes final releases of Firm Capacity
on any of the following Oil Pipelines or agreements: 8” Ayacucho – Galán, 16” Ayacucho – Coveñas,
24” Ayacucho – Coveñas or Use of Port for Crude at Coveñas.



EIGHT.- The Parties understand that
the other clauses of the Agreement shall remain current in all aspects not expressly amended in this Addendum No. 6.



In attestation of the above, this Addendum No.
6 is signed by the undersigned, in Bogotá D.C., on April twenty-fifth (25th), 2016.



|By ECOPETROL,                    |  | By CENIT,                
|-------------------------------- |  | -------------------------
|                                 |  |                          
|/s/ Juan Carlos Echeverry Garzón |  | /s/ Thomas Rueda Ehrhardt
|Juan Carlos Echeverry Garzón     |  | Thomas Rueda Ehrhardt    
|Chief Executive Officer          |  | Chairman                 



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