II. - Dans un souci didactique qui est malheureusement exceptionnel en matière d'arbitrage, la sentence expose en termes généraux trois principes de lex mercatoria. Le respect du premier, selon lequel les prestations contractuelles doivent rester équilibrées dans les transactions internationales, est habituellement assuré par l'insertion dans les contrats de clauses permettant leur adaptation aux modifications des circonstances extérieures. Tel est l'objet des clauses de „hardship“ (cf. B. Oppetit, „L'adaptation des contrats internationaux aux changements de circonstances: la clause de Hardship“: Clunet 1974, 704; V. Également les divers exemples de clauses reproduites in Droit et pratique du commerce international 1975, 512). Les clauses de „maintien de valeur“, qui garantissent les parties contre les fluctuations monétaires répondent à des préoccupations voisines (cf. S.A. Silard „Clauses de maintien de la valeur dans les transactions internationales“: Clunet 1972, 214). La présence presque automatique de clauses de ce type dans les contrats internationaux amène a contrario les arbitres à se montrer particulièrement rigoureux chaque fois qu'une partie cherche à se dégager d'une de ses obligations contractuelles au nom du principe „Rebus sic stantibus“, sans pouvoir invoquer une clause de révision ou d'indexation. Les arbitres tendent en effet à présumer que c'est sciemment que les parties se sont abstenues d’inclure de telles clauses dans leur convention et qu'en conséquence le principe „Pacta sunt servanda“, autre règle fondamentale de la lex mercatoria doit être appliqué sans restriction. Cette tendance est confortée par l'idée, soulignée dans la sentence ici rapportée, que les parties doivent veiller à la sauvegarde de leurs intérêts (cf. sentences rendues dans l'affaire n° 1512 en 1971: Clunet 1974, 905, dans l'affaire n° 2216 en 1974: Clunet 1975, 917, dans l'affaire n° 2404 en 1975, infra, p. 995). Mais lorsque, comme dans la présente espèce, les parties ont prévu une clause de révision, celle-ci reçoit les plus larges effets, l'usage venant cette fois renforcer et compléter une volonté exprimée de façon positive.
Observations. – I – Underlining the absence of a contract drawn up in due form between the parties, the arbitrator chooses to consider the intention of the parties and to determine their respective obligations in the light of the documents that were exchanged between them and especially of the “general principles of law and equity that are bound to govern international commercial transactions“. The impossibility to find out the answer to a legal problem in the wording of a contract's clauses leads the arbitrator to take into consideration two fundamental elements of the emerging lex mercatoria which are: the general principles of law on the one hand and the principle of equity on the other hand (on the fact that the adherence to the general principles of law is itself considered as a custom in international commerce and as an integral part of the lex mercatoria, cf. our observations in the judgement of 1969 in case No. 1641: Clunet 1974, 888). The approach of the arbitrator reveals the systematic nature of the lex mercatoria. Setting aside the existence of self-regulatory contracts, the lex mercatoria constitutes a body of norms, which, like the national legal systems, contains suppletive rules that can be applied in case the intention of the parties has not adequately been expressed. These anational rules are much more in harmony with the contractual conditions the parties provided for than national suppletive rules, as the former are nothing else than the reflection of customs generally adhered to. That’s why arbitrators can pretend to find in the lex mercatoria principles which the parties would probably have incorporated into the contract had they taken care to put it in writing.
II. –For didactic purposes, which are unfortunately the exception in arbitration matters, the sentence exposes, in general terms, three principles of lex mercatoria. The adherence to the first, which says that in international transactions contractual obligations must be well-balanced, is usually assured by contract clauses which allow the contracts’ adaptation to changing external conditions. This is also the purpose of including so-called “hardship” clauses (cf. B. Oppetit, “L’adaptation des contrats internationaux aux changements de circonstances: la clause de Hardship”: Clunet 1974, 704; seealso various examples of clauses reproduced in Droit et pratique du commerce international 1975, 512). “Stable-value” clauses which protect the parties against monetary fluctuations deal with comparable concerns. (cf. S.A. Silard “Clauses de maintien de la valeur dans les transactions internationales”: Clunet 1972, 214). The almost automatic inclusion of such clauses in international contracts leads a contrario the arbitrators to act in an especially strict way each time one party wants to be released from a contractual obligation by relying on the “Rebus sic stantibus” principle, without being able to invoke a revision or index clause. In fact, arbitrators tend towards the opinion that in such a case the parties did deliberately not include these clauses and that, therefore, the principle “Pacta sunt servanda”, another fundamental rule of the lex mercatoria, has to be applied without restriction. This tendency is supported by the idea that the parties themselves have to protect their interests, which is underlined in the arbitral award here mentioned (cf. the arbitral awards in case No. 1512 in 1971: Clunet 1974, 905, in case No. 2216 in 1974: Clunet 1975, 917, in case No. 2404 in 1975, infra, p. 995). But if, as in the present case, the parties provided for a revision clause, this clause has to be applied in the largest manner, the usage of which being considered as the reinforcement and concretization of an explicitly expressed intention of the parties.