NEW YORK (Bloomberg) — Bermuda-based Frontline Ltd., the world’s second- biggest tanker operator, had the rating on its shares upgraded to “buy” from “hold” by New York-based investment bank Dahlman Rose & Co. after selling shares in its Sealift Ltd. unit.Sealift, a company created by Frontline to operate oil-rig transporters, raised $180 million in a share sale in which its parent bought a 33 percent stake. Frontline $167 million profit selling six single-hulled oil tankers to the Sealift unit for conversion into oil-rig transporters.

Frontline and other owners are racing against a 2010 United Nations deadline on using tankers with only one layer around their cargo tanks, known as single-hulls. By converting those ships to alternative uses, Frontline will be able to extend the vessels’ working lives instead of having to sell them for scrap.