Oceangoing vessels of less than 400 gross tons must be able to retain all oily mixtures until it can be discharged to a reception facility. Alternatively, vessels may carry approved oily-water separator (OWS) equipment to separate oil from the water and discharge the water overboard, as long as the effluent contains less than 15 parts per million (ppm) oil and meets other criteria provided in 33 CFR 151.10.

The regulations require oceangoing vessels of less than 400 gross tons to:

  • Have the capacity to retain all oily mixtures onboard and be equipped to discharge said mixtures to a reception facility
  • Have approved OWS equipment for processing oily mixtures from bilges or fuel oil tank ballast and discharges into the sea.

Both 33 CFR 155.350 and 33 CFR 151.10 apply to US vessels wherever they are and to foreign flagged vessels within twelve miles of the US shoreline.


The discharge of oily mixtures from oceangoing vessels overboard via "decanting" is not allowed. "Decanting" or "skimming" regard pumping bilge water from below any perceived oily film or sheen on the bilge water’s surface. This practice is a violation of 33 CFR 151.10 and 33 CFR 155.350.

Operating of a vessel without pollution prevention equipment may lead to civil penalties, judicial civil action, and/or Captain of the Port orders directing remedial action. In addition, unlawful discharges of oily mixtures may cause criminal proceedings .

Therefore, the US Coast Guard recommends that vessel operators the following:

  • Identify and reduce sources of liquid entering machinery space bilges;
  • Ensure material conditions do not result in water entering machinery spaces from non-machinery spaces resulting from leaks or free communication;
  • Voyage planning for the safe and lawful maintenance and disposal of oily mixtures.