Maritrans Inc. has obtained a patent on its proprietary process for rebuilding single-hull tank ships and converting them into double-hull vessels. With the most recent patent, Maritrans has now patented the double-hull conversion process for both barges and tank ships. The U.S. Oil Pollution Act of 1990, as well as the International Convention for the Prevention of Pollution from Ships (MARPOL), each require the retirement of single-hull tank vessels. In January of 2001, Maritrans announced that it had received the first of three patents for internal double-hull conversions of single-hull barges. These Maritrans patents involved pre-fabrication of large tank structures that are inserted into the existing hull, with a trunk deck extending above the pre-existing deck.