(Bloomberg) ? Frontline Ltd., the world?s biggest oil carrier by capacity, said its Sea Production Ltd. unit that turns tankers into floating oil-platforms raised $180 million in a share sale.

Frontline, led by Norwegian billionaire John Fredriksen, kept a 28 percent stake in Sea Production following the sale, Hamilton, Bermuda-based Frontline said in a statement to the Oslo Stock Exchange. Singapore?s Keppel Corp., the world?s biggest maker of shallow-water oil rigs, took 5 percent.

Sea Production will transform tankers into so-called floating storage, production and offloading ships, or FPSOs. The vessels collect, process and store crude oil found in remote offshore locations. FPSOs can be used for 15 years. Under international rules that will come into force in 2010, single- hulled oil tankers will be banned from carrying oil. Sea Production will buy the Frontline tanker Front Puffin, which is being converted into an FPSO in Singapore. It will also acquire two tankers for $18 million each from Seatankers Management Co., Fredriksen?s closely held company in Cyprus, and another from Seadrill Ltd., which is also led by Fredriksen, for $90 million.