Results of an analysis to estimate potential oil outflow from tankers in the event of groundings and collisions is presented. Three baseline tanker types are considered: pre-MARPOL (COW), MARPOL ＇73 (SBT only), MARPOL ＇73/＇78 (PL/SBT) before and after these tankers have been retrofitted with various combinations of pollution prevention measures. Specifically the analysis examines four tanker sizes, 46600, 71000, 152000 and 268000 dwt, and various pollution measures - protectively located spaces (PL/spaces) in various ballast arrangements and with clean ballast tanks (CBTs), hydrostatically balanced Loading (HBL), probabilistically located HBL, combinations of HBL and PL/spaces, double bottom or double side retrofits, and replacement of the tanker with a double hull vessel. Additionally, oil outflow estimates are presented for a US coastal and an ocean going barge of over 5000 gt with and without PL/spaces, PL/SBT, and HBL. The accidental oil outflow estimates are developed in accordance with probabilistic and deterministic models of IMOs MARPOL Annex I Regulations 13F and 13G. The accidental oil outflow estimates presented in the paper may provide oil spill response and related organizations with information to assist in planning for oil spill response activities.