This article is an extract from The Investment Treaty Arbitration Review, 7th Edition. Click here for the full guide.


I Introduction

An arbitral tribunal constituted on the basis of an agreement to arbitrate in an investment treaty, such as a bilateral investment treaty (BIT) or a multilateral agreement such as the Energy Charter Treaty, will need to engage in treaty interpretation to discharge its duty to decide the dispute. When tribunals are called to interpret a 'treaty',2 they turn to the Vienna Convention on the Law of Treaties 1969 (VCLT).3 The VCLT is the product of an extensive codification process of the International Law Commission led by distinguished Special Rapporteurs.4 It has been ratified by 116 states and even some non-ratifying states (such as the United States) recognise that parts of the VCLT reflect customary international law.5 Equally, tribunals consider certain parts of the Convention as reflective of customary international law on matters of treaty interpretation.6

The VCLT addresses a range of fundamental topics on the law of treaties. The provisions of the Convention that concern interpretation are within Part III (Observance, Application and Interpretation of Treaties), Section 3 (Interpretation of Treaties) and Article 31 (General rule of interpretation) and Article 32 (Supplementary means of interpretation).

This chapter addresses each of the four limbs of Article 31 and Article 32, and uses relevant and recent case law to draw out their key features in guiding interpretation of treaties.

II Article 31

The drafters of the VCLT made clear that there is no hierarchy among the four sub-articles of Article 31. Instead, together, they constitute the general rule (singular, not plural) of interpretation.7

i Article 31(1)

Article 31(1) states:

A treaty shall be interpreted in good faith in accordance with the ordinary meaning to be given to the terms of the treaty in their context and in the light of its object and purpose.

Article 31(1) contains three separate principles.8 The first, good faith interpretation, 'flows directly from the rule pacta sunt servanda'.9 The second is that the text is presumed to be the 'authentic expression of the intentions of the parties'.10 The third is that the ordinary meaning of a term is to be determined not in the abstract but in light of the treaty's context and object and purpose.11 The maxim ut res magis valeat quam pereat (or the 'principle of effectiveness') is also embodied in Article 31(1), insofar as it reflects a true general rule of interpretation.12

A straightforward application of Article 31(1) can be seen in Murphy International v. Ecuador. Ecuador objected to the tribunal's jurisdiction over the dispute. It argued that, at the time Murphy International consented to arbitration by the International Centre for Settlement of Investment Disputes (ICSID), there was no consent on the part of Ecuador. Rather, by the time the claimant consented to arbitration (on 29 February 2008), Ecuador had already notified ICSID (on 4 December 2007), pursuant to Article 25(4) of the Convention on the Settlement of Investment Disputes between States and National of Other States (the ICSID Convention),13 that it would not consent to arbitrate the class of disputes in which the claimant's claims fell.14

The tribunal disagreed. After quoting the text of Article 25(4) of the ICSID Convention, and referring to the general rule in Article 31(1) of the VCLT, the tribunal found that an Article 25(4) notification may not unilaterally modify the consent given in the BIT.15 Article 25(4) states that '[a]ny Contracting State may . . . notify the Centre of the class or classes of disputes which it would or would not consider submitting to the jurisdiction of the Centre'. Ecuador's communication, therefore, was nothing more than a 'notification'.16 Because the language of Article 25(4) was clear and unambiguous, the tribunal saw no need to resort to 'supplemental' means of interpretation (i.e., under Article 32 of the VCLT).17

ii Article 31(2)

Article 31(2) defines the word 'context' that is found in Article 31(1).18 It states:

The context for the purpose of the interpretation of a treaty shall comprise, in addition to the text, including its preamble and annexes:(a) any agreement relating to the treaty which was made between all the parties in connection with the conclusion of the treaty;(b) any instrument which was made by one or more parties in connection with the conclusion of the treaty and accepted by the other parties as an instrument related to the treaty.

The text, including its preamble and annexes

In practice, a treaty's object and purpose are among the 'primary guides' for interpretation, and it is often derived from the preamble of the treaty.19 The preambles of investment treaties tend to highlight the positive role of foreign investment and the link between an investor-friendly climate and the flow of foreign investment.20 For example, in Al-Warraq v. Indonesia, the tribunal referred to the preamble of the OIC Agreement21 – which speaks of a 'favourable climate for investment' – when it found that the most-favoured nation provision in the OIC Agreement allowed a party to import the fair and equitable treatment standard from another BIT.22

More recently, tribunals have questioned the utility of referring to the preamble of a BIT given the general terms in which they tend to be couched. As the tribunal explained in Kappes v. Guatemala:

It is certainly true . . . that the DR-CAFTA [Dominican Republic–Central America Free Trade Agreement] Preamble refers to a goal to “ENSURE a predictable commercial framework for business planning and investment[.]” . . . But that observation cannot be the end of the story. Every treaty creates a varied and nuanced balance between extending protections and limiting or conditioning those protections. It would be too facile to simply advert to the general notion of investor protection as a catch-all tool (or a proverbial finger-on-the-scale) to resolve all disputed issues regarding the extent, limits or conditions on protections.23

Agreements or instruments made by some or all of the parties

There are two other building blocks of the 'context' in which words are to be interpreted: an agreement relating to the treaty made by both parties in connection with the conclusion of the treaty, and an instrument made by one party and accepted by the other parties as an instrument related to the treaty. The guiding rationale here is that a 'unilateral' document does not form part of the context; it must have been made in connection with the conclusion of the treaty and the other parties must have accepted it in relation to the treaty.24

Tribunals have not always interpreted these provisions consistently. In Fraport v. Philippines, the tribunal had to determine whether an investment needed to be made in accordance with the host state's laws to qualify for substantive protection. Article 1(1) of the Germany–Philippines BIT provided that 'investment' shall mean 'any kind of asset accepted in accordance with the respective laws and regulations of either Contracting State'.25 In interpreting the word 'investment', the tribunal relied on, among other things, the terms of an 'instrument of ratification' that the Philippines had exchanged with Germany three months after the conclusion of the BIT (the Philippine Instrument).26 Germany had exchanged its own instrument with the Philippines at the same time.27 The tribunal relied on certain wording in the Philippine Instrument to support its conclusion that Article 1(1) 'explicitly and reiteratedly required that an investment . . . had to be in accordance with the host state's law'.28

On annulment, the ad hoc committee criticised the tribunal's reliance on the Philippine Instrument.29 It explained that the Philippine Instrument was a 'unilateral act' by which the Philippines had expressed its consent to be bound by the treaty; it was not an interpretative declaration intimated to Germany for its acceptance.30 That may be true: the Philippine Instrument certainly did not constitute a 'subsequent agreement' for the purposes of Article 31(2)(a) of the VCLT. However, it does appear to fall within Article 31(2)(b), which refers to an 'any instrument which was made by one or more parties in connection with the conclusion of the treaty and accepted by the other parties as an instrument related to the treaty'.31 First, the Philippine Instrument was made 'in connection with the conclusion of the treaty' since it pertained to ratification of the Germany–Philippines BIT. Second, Germany 'accepted' that the Philippine Instrument was 'related' to that BIT, not least because it conveyed its own instrument of ratification to the Philippines at the same time. Notably, unlike Article 31(2)(a), Article 31(2)(b) does not feature the word 'agreement'.

iii Article 31(3)

Article 31(3) states:

There shall be taken into account, together with the context:(a) any subsequent agreement between the parties regarding the interpretation of the treaty or the application of its provisions;(b) any subsequent practice in the application of the treaty which establishes the agreement of the parties regarding its interpretation;(c) any relevant rules of international law applicable in the relations between the parties.

Subsequent agreement between the parties – Article 31(3)(a)

The tribunal in Methanex had little difficulty applying this provision to a note of interpretation issued by the Federal Trade Commission (the FTC). Under Article 1131(2) of the North American Free Trade Agreement (NAFTA), an interpretation by the FTC of a NAFTA provision is binding on a NAFTA tribunal. On 31 July 2001, shortly after the end of an oral hearing in Methanex that month, the FTC adopted certain 'interpretations of Chapter Eleven in order to clarify and reaffirm the meaning of certain of its provisions'.32 The United States argued that an FTC interpretation was a 'subsequent agreement' for the purposes of Article 31(3)(a), which the tribunal ought to take into account when interpreting certain provisions of NAFTA.33 The tribunal readily accepted that the FTC interpretation was properly characterised as a 'subsequent agreement', and added that such an agreement need not be concluded with the formal requirements of a treaty.34

More recently, tribunals have had to grapple with Article 31(3)(a) in the context of declarations made by EU Member States about the compatibility with EU law of investor-state dispute settlement (ISDS) clauses in intra-EU BITs (that is, a BIT between two EU Member States). In March 2018, the Court of Justice of the European Union published its preliminary ruling in Slovak Republic v. Achmea BV, in which it held that the ISDS provision in Article 8 of the Netherlands–Slovakia BIT was incompatible with EU law. In January 2019, 23 EU Member States issued declarations on the legal consequences of the Achmea decision, affirming that 'all investor-State arbitration clauses contained in bilateral investment treaties concluded between Member States are contrary to Union law and thus inapplicable'35 (the Achmea declarations).

In GPF v. Poland,36 the respondent argued that the Achmea declarations constituted a 'subsequent agreement' and thus rendered Article 9 of the Poland–Luxembourg BIT, the ISDS provision, inapplicable. The tribunal disagreed. Citing a commentary on an earlier draft of the VCLT, it explained that a 'subsequent agreement' for the purposes of Article 31(3)(a) had to relate to 'understandings reached by States during negotiations of a relevant treaty'.37 The Achmea declarations did not reflect such an understanding: at the time the BIT was concluded, the states themselves did not indicate any concern about the incompatibility between Article 9 of the BIT and EU law. Instead, the Achmea declarations merely reflected the 'political will' to terminate intra-EU BITs as of 2019.38 Further, the tribunal noted that the title of the Achmea declarations themselves – 'Declaration . . . on the Legal Consequences of the Judgment of the Court of Justice in Achmea and on Investment Protection in the European Union' – suggested that the EU Member States sought to explain the legal consequences of the Achmea decision, rather than interpret the dispute settlement clauses in intra-EU investment treaties.39

In Ekosol v. Italy, the tribunal reached the same conclusion about the Achmea declarations in the context of a case under the Energy Charter Treaty (ECT).40 In addition, the tribunal pointed out that Article 31(3)(a) requires that the 'subsequent agreement' must be between all the parties to the relevant treaty.41 The two states who had a 'stake' in the Ekosol arbitration could not bilaterally change the terms of the ECT.42 As the tribunal put it:43

VCLT Article 31(3)(a) is not . . . a trump card to allow States to offer new interpretations of old treaty language, simply to override unpopular treaty interpretations based on the plain meaning of the terms actually used.

Subsequent practice in the application of the treaty – Article 31(3)(b)

According to Article 31(3)(b), a tribunal shall also take into account any 'subsequent practice' in the application of the treaty that establishes the agreement of the parties regarding its interpretation. This provision is informed by the idea that subsequent practice in the application of a treaty constitutes objective evidence of the parties' understanding of the treaty's meaning.44

One recurring issue in case law is whether a position taken by a state in previous arbitrations constitutes a 'subsequent practice' for the purpose of Article 31(3)(b). In Urbaser v. Argentina, which concerned the Spain–Argentina BIT, Argentina referred to a position taken by Spain in the Maffezini case.45 That was not enough to constitute 'subsequent practice': it only showed what Spain's counsel argued in a particular arbitration; it did not, without more, represent Spain's – let alone Spain's and Argentina's – interpretation of the provisions of the BIT.46 In Telefónica v. Argentina, Argentina took its argument a step further. It pointed to the 'parallel' and 'similar' positions taken by Spain in Maffezini and by Argentina in Siemens and Gas Natural on the interpretation of Article IV.2 of the Spain–Argentina BIT as indicative of 'subsequent acts carried out by the parties'.47 Once again, the tribunal was not convinced. It explained that Spain's and Argentina's positions in the above-mentioned cases did not amount to their 'application' of the BIT, and their statements were not directed towards each other, and so could not be an 'agreement'.48

Yet, the comments of the tribunals in these cases, particularly in Telefónica, sat uneasily with the tribunal in Kappes v. Guatemala, which considered the interpretation of Article 10.16.1(a) of the DR-CAFTA, a multilateral treaty between the United States and several states, largely in Central America. It drew attention to the fact that Article 31(3)(b) refers to 'any' subsequent practice in the application of the treaty, and explained that a demonstration that all state parties to a particular treaty had expressed a common understanding in their submissions to (separate) arbitral tribunals 'could be compelling evidence of subsequent practice'.49 However, there had not yet been any unanimous expression of views about the scope and implications of Article 10.16.1(a) of the DR-CAFTA, and so the tribunal did not rely on prior statements by either state in the interpretation of the DR-CAFTA.

Relevant rules of international law – Article 31(3)(c)

Finally, Article 31(3)(c) directs tribunals to take into account 'any relevant rules of international law applicable in the relations between the parties'.

The interpretation of this provision in international law is not settled. In the Oil Platforms case, three Iranian oil platforms and a US Navy warship were destroyed when the ship struck a mine in international waters. Among other things, Iran claimed that the United States had violated Article XX of the Treaty of Amity. The International Court of Justice decided that it should take into account the entirety of international law relating to the use of force in interpreting this provision.50 In her Separate Opinion, Judge Rosalyn Higgins criticised such a reading of Article 31(3)(c) on the basis that it ignored the limited 'context' that, there, was that of an economic and commercial treaty.51

Investment arbitration tribunals appear to have adhered to a narrower understanding of this provision, preferring to take into account any relevant rules of 'customary international law'52 rather than international law as a whole. Further, attempts to broaden the scope of this provision have been unsuccessful. In RosInvestCo v. Russia, the claimant urged the tribunal to adopt a 'dynamic' approach to the interpretation of the 1989 UK–USSR BIT, one that would have given 'full weight' to the events that post-dated the conclusion of the BIT, notably, the 'dissolution of the USSR, the emergence of the Russian Federation . . . and the radically different economic, trading and investment policies adopted by the Russian Federation'.53 To support its argument, the claimant referred to cases that concerned human rights treaties and treaties concerning the constituent instruments of international organisations.54

The tribunal rejected the claimant's argument. It distinguished the cases on which the claimant relied on the basis that they concerned multilateral treaties that naturally called for a 'dynamic' approach. First, human rights treaties represented the very archetype of treaty instruments in which the contracting parties must have intended that the underlying principles should be understood and applied 'in the light of developing social attitudes'.55 Second, international organisations had to confront ever-changing problems and circumstances, and so a degree of evolutionary adaptation was the 'only realistic approach' to realising the underlying purposes of the organisation as laid down in its constituent instrument.56

Here, the tribunal explained, the BIT was a matter of specific consent by two parties, the United Kingdom and the USSR. The reference in Article 31(3)(c) of the VCLT to relevant rules of international law that are 'applicable in the relations between the parties' must:

be taken as a reference to rules of international law that condition the performance of the specific rights and obligations stipulated in the treaty – or else it would amount to a general licence to override the treaty terms that would be quite incompatible with the general spirit of the Vienna Convention as a whole.57

iv Article 31(4)

Article 31(4) states that:

A special meaning shall be given to a term if it is established that the parties so intended.

This sub-article caters for a situation in which, 'notwithstanding the apparent meaning of a term in its context, the parties intended it to have a special meaning'.58 The party invoking the special meaning has the burden of proof.59 There is little investment arbitration case law on this provision at present. It was unsuccessfully invoked in Canfor v. United States, in which the tribunal held that a letter from a trade official of one NAFTA party to a private company that addressed the interpretation of an intergovernmental agreement with another NAFTA party was not evidence that a 'special meaning' had been given to a term for the purposes of Article 31(4).60

III  Article 32

Article 32 states that:

Recourse may be had to supplementary means of interpretation, including the preparatory work of the treaty and the circumstances of its conclusion, in order to confirm the meaning resulting from the application of article 31, or to determine the meaning when the interpretation according to article 31:
  1. (a) leaves the meaning ambiguous or obscure; or
  2. (b) leads to a result which is manifestly absurd or unreasonable.

Article 32 is entitled 'Supplementary means of interpretation'. It is a means of interpretation that is 'supplementary' to the 'General rule of interpretation' set forth in Article 31. The drafters explained that the principal distinction between Articles 31 and 32 is the degree to which the various means of interpretation contained therein accurately reflect the parties' agreement:

The elements of interpretation in article [31] all relate to the agreement between the parties at the time when or after it received authentic expression in the text. Ex hypothesi this is not the case with preparatory work [i.e. Article 32] which does not, in consequence, have the same authentic character as an element of interpretation, however valuable it may sometimes be in throwing light on the expression of the agreement in the text. Moreover, it is beyond question that the records of treaty negotiations are in many cases incomplete or misleading, so that considerable discretion has to be exercised in determining their value as an element of interpretation.61

i Threshold issue – recourse to supplementary means of interpretation

A threshold issue arises as to when a tribunal may have recourse to 'supplementary means of interpretation'. Perhaps because of the word 'or', a textual reading of Article 32 suggests that supplementary means it may be considered in three circumstances, namely:

  1. to confirm the meaning resulting from the application of Article 31;
  2. to determine the meaning when the application of Article 31 leaves the meaning ambiguous or obscure; or
  3. to determine the meaning when the application of Article 31 leads to a 'manifestly absurd or reasonable' result.62

Not all tribunals interpret Article 32 in this way; some confine Article 32 to a confirmatory role. For example, in Noble Ventures v. Romania, the tribunal said:

[R]ecourse may be had to supplement means of interpretation, including the preparatory work and the circumstances of its conclusion, only in order to confirm the meaning resulting from the application of the aforementioned methods of interpretation.63

On either reading, there should generally be no need to resort to supplementary means of interpretation if the ordinary meaning of words is clear and makes sense in the context.64 The drafters of the VCLT stopped short of prohibiting recourse to supplementary means in such situations:65 the Commission felt that it would be 'unrealistic and inappropriate' to state that no recourse whatever may be had to extrinsic means of interpretation.

Whatever the theoretical importance of this threshold issue, in practice, resort to 'supplementary means' like the travaux préparatoires seems to be determined primarily by their availability.66 In Malaysian Historical Salvors v. Malaysia, the ad hoc committee explained:

[C]ourts and tribunals interpreting treaties regularly review the travaux préparatoires whenever they are brought to their attention; it is mythological to pretend that they do so only when they first conclude that the term requiring interpretation is ambiguous or obscure.67

ii Resort to supplementary means

In Austrian Airlines v. Slovakia, the tribunal resorted to supplementary means to interpret Article 8 of the Austria–Slovakia BIT,68 which concerned the scope of the dispute resolution clause. Article 8 stated (in its relevant part) as follows:

Any disputes arising out of an investment, between a Contracting Party and an investor of the other Contracting Party, concerning the amount or the conditions of payment of a compensation pursuant to Article 4 of this Agreement . . . [shall be decided by] arbitral proceedings in accordance with the UNCITRAL Arbitration Rules.69

Article 4 stated (in it relevant parts):

The investor shall have the right to have the legitimacy of the expropriation reviewed by the competent authorities of the Contracting Party which prompted the expropriation.The investor shall have the right to have the amount of the compensation and the conditions of payment reviewed either by the competent authorities of the Contracting Party which prompted the expropriation or by an arbitral tribunal according to Article 8 of this Agreement.

The tribunal began by discerning the ordinary meaning of the words used in Articles 8 and 4. It concluded that access to arbitration was intended to be limited to the 'amount and conditions of the indemnity, as opposed to the . . . lawfulness' of expropriation.70 The claimant argued that this reading was inconsistent with the object and purpose of the BIT – which was the protection of foreign investors – because it enabled the local courts of the host state to unilaterally avoid arbitration if they denied a claim for expropriation.71

The tribunal was unmoved, on the basis that Articles 4 and 8 were clear on the allocation of responsibility between the local courts and any arbitral tribunal. It then referred to the travaux préparatoires to confirm its understanding. It reviewed the negotiating history and earlier drafts of the BIT and found that the wording in Article 8 was the result of a process by which the scope of disputes subject to arbitration was purposefully restricted.72

Finally, although Article 32 identifies 'preparatory work' and the 'circumstances of [the treaty's] conclusion' as two examples of supplementary means of interpretation, it is clear from the way it was drafted that there may be other kinds of supplementary means. As the HICEE v. Slovakia tribunal put it, 'the category of admissible supplementary means is not a closed one'.73 In that case, the tribunal suggested that the other supplementary means that it may refer to included 'all available material that it finds to be relevant, significant, and at the same time reliably instructive as to the meaning and intention behind the words used in the Agreement'.74

IV Conclusion

For investment treaty tribunals, Articles 31 and 32 of the VCLT are important in the interpretation of BITs and multilateral agreements. As Dolzer and Schreuer explain: 'Most tribunals start by invoking Article 31 of the Vienna Convention on the Law of Treaties (VCLT) when interpreting treaties.'75 As this chapter has shown, although tribunals strive to faithfully apply the terms of Articles 31 and 32 of the VCLT, the challenge for tribunals remains the correct and consistent application of the Convention in interpreting those treaties.