The DC-6B was en route from South Caicos to Port-au-Prince, Haiti when one engine was shut down after running out of oil. Subsequently two other engines were shut down as well for the same reason. The aircraft ditched. PROBABLE CAUSE: pilot in command – attempted operation w/known deficiencies in equipment pilot in command – inadequate preflight preparation and/or planning miscellaneous acts,conditions – oil exhaustion-engine lubrication system pilot in command – improper in-flight decisions or planning FACTORS: instruments/equipment and accessories – communications and navigation equipment: transmitters and/or receivers miscellaneous acts,conditions – material failure miscellaneous acts,conditions – failure of two or more engines miscellaneous acts,conditions – aircraft came to rest in water complete power loss – unknown/not reported