An oiler is one of the most junior crewmember in the engine room of a ship (senior only to a wiper). Their role consists mainly of keeping machinery lubricated.
In the United States Merchant Marine, in order to be occupied as a oiler a person has to have a Merchant Mariner's Document issued by the United States Coast Guard. Because of international conventions and agreements, all oilers who sail internationally are similarly documented by their respective countries. Flag of the United States Merchant Marine The U.S. Merchant Marine flag flown at the American Merchant Marine Veterans Memorial in Point Park in Ashtabula, Ohio The United States Merchant Marine comprise the merchant ships that are used to transport both imports and exports during peace time and serves... The United States Coast Guard (USCG) is a branch of the United States armed forces involved in maritime law enforcement, mariner assistance, search and rescue, and national defense, among other duties of coast guards elsewhere. ...