OSLO (Bloomberg) — Fred. Olsen Production ASA, the Norwegian oil-services company, sold a storage vessel that was once the world's largest crude tanker.

An unidentified Asian buyer purchased Knock Nevis, used now to hold oil rather than transport it, Oslo-based Fred. Olsen Production said today in a stock-exchange statement. The new owner also will use the vessel to store crude.

The 1976-built ship, previously called Seawise Giant, Happy Giant and most recently Jahre Viking, has a carrying capacity of 564,650 deadweight tons, according to Lloyds Register-Fairplay data on Bloomberg. That would be enough to ship or store more than four million barrels of crude, equating to about two days of Mexican oil demand.

Knock Nevis was originally constructed in response to the closing of Egypt's Suez Canal from the 1960s to the 1970s, said Mark Jenkins, a London-based analyst at Simpson Spence & Young Ltd., the world's second-largest shipbroker. Once the waterway reopened, vessels of Knock Nevis' size lost commercial attraction for charters because most European, US and Asian ports were too small for them to dock, according to Jenkins.

That's why the ship spent most of its trading life storing oil rather than delivering it, he said. The vessel remains the biggest ever built, Jenkins said. Fred. Olsen Production will book a fourth-quarter gain of about $6 million from the sale, according to the statement.

The TI Oceania and the TI Europe, which have carrying capacities of about 442,000 deadweight tons, are the biggest oil tankers operating today, Jenkins said.