Article 35. Treaties providing for obligations for third States
An obligation arises for a third State from a provision of a treaty if the parties to the treaty intend the provision to be the means of establishing the obligation and the third State expressly accepts that obligation in writing.
Article 36. Treaties providing for rights for third States
1. A right arises for a third State from a provision of a treaty if the parties to the treaty intend the provision to accord that right either to the third State, or to a group of States to which it belongs, or to all States, and the third State assents thereto. Its assent shall be presumed so long as the contrary is not indicated, unless the treaty otherwise provides.
2. A State exercising a right in accordance with paragraph 1 shall comply with the conditions for its exercise provided for in the treaty or established in conformity with the treaty.
Article 37. Revocation or modification of obligations or rights of third States
1. When an obligation has arisen for a third State in conformity with Article 35, the obligation may be revoked or modified only with the consent of the parties to the treaty and of the third State, unless it is established that they had otherwise agreed.
2. When a right has arisen for a third State in conformity with Article 36, the right may not be revoked or modified by the parties if it is established that the right was intended not to be revocable or subject to modification without the consent of the third State.
Article 38. Rules in a treaty becoming binding on third States through international custom
Nothing in articles 34 to 37 precludes a rule set forth in a treaty from becoming binding upon a third State as a customary rule of international law, recognized as such.
PART IV - AMENDMENT AND MODIFICATION OF TREATIES
Article 39. General rule regarding the amendment of treaties
A treaty may be amended by agreement between the parties. The rules laid down in Part II apply to such an agreement except in so far as the treaty may otherwise provide.
