MARPOL 73/78 Annex 1
The International Convention for the Prevention of Pollution from Ships (MARPOL) is the main international convention covering prevention of pollution of the marine environment by ships from operational or accidental causes. The Convention includes regulations aimed at preventing and minimizing pollution from ships - both accidental pollution and that from routine operations - and currently includes six technical Annexes. Special Areas with strict controls on operational discharges are included in most Annexes.
Annex I - Regulations for the Prevention of Pollution by Oil, covers prevention of pollution by oil from operational measures as well as from accidental discharges.
More information here.