This article examines whether or not the FET standard has become a rule of customary international law. The article contains the first empirical analysis of this question based on the two conditions under which a treaty-based norm can transform into a customary rule. The article will argue that the standard has not become a rule of custom. While the practice of States to include FET clauses in their BITs can be considered as general, widespread and representative, it is not uniform and consistent. There are in fact many different types of FET clauses and these variations matter a great deal. Also, the practice of States outside treaties shows that they rarely offer FET protection to foreign investors under their foreign investment laws. There is no indication that States parties to BITs believe that they have an obligation (opinio juris) under international law to provide FET protection to each other’s investors.

中文翻译：

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公平公正待遇标准是否已成为习惯国际法规则？：

本文探讨 FET 标准是否已成为习惯国际法规则。本文根据基于条约的规范可以转变为习惯规则的两个条件对这个问题进行了首次实证分析。文章将争辩说，该标准尚未成为习惯规则。虽然各国在其双边投资条约中包含 FET 条款的做法可以被认为是普遍的、广泛的和具有代表性的，但它并不统一和一致。事实上，有许多不同类型的 FET 条款，这些变化非常重要。此外，条约之外国家的实践表明，它们很少根据其外国投资法向外国投资者提供 FET 保护。