Artikel 18

1. Subject to paragraph 4, the aggregate amount of the annual contributions payable in respect of contributing oil received in a single Contracting State during a calendar year shall not exceed 20% of the total amount of annual contributions pursuant to this Protocol in respect of that calendar year.
2. If the application of the provisions in article 11, paragraphs 2 and 3, would result in the aggregate amount of the contributions payable by contributors in a single Contracting State in respect of a given calendar year exceeding 20% of the total annual contributions, the contributions payable by all contributors in that State shall be reduced pro rata so that their aggregate contributions equal 20% of the total annual contributions to the Supplementary Fund in respect of that year.
3. If the contributions payable by persons in a given Contracting State shall be reduced pursuant to paragraph 2, the contributions payable by persons in all other Contracting States shall be increased pro rata so as to ensure that the total amount of contributions payable by all persons liable to contribute to the Supplementary Fund in respect of the calendar year in question will reach the total amount of contributions decided by the Assembly.
4. The provisions in paragraphs 1 to 3 shall operate until the total quantity of contributing oil received in all Contracting States in a calendar year, including the quantities referred to in article 14, paragraph 1, has reached 1,000 million tons or until a period of 10 years after the date of entry into force of this Protocol has elapsed, whichever occurs earlier.