Royal Dutch Shell Plc, Europe’s biggest oil company, halted plans to build a $20 billion gas-to-liquids plant in Louisiana, citing the potential cost and uncertainty about future crude and natural gas prices.

The project would have used natural gas to produce 140,000 barrels a day of liquid fuels and other products normally made from oil, The Hague-based company said in a statement Thursday. Despite ample U.S. gas supplies from a boom in shale production, gas-to-liquids isn’t “a viable option for Shell in North America,” the company said.

Shell started the first commercial gas-to-liquids plant in 1993, using a process developed in Germany and used to make fuels during World War II. The company completed the $19 billion Pearl gas-to-liquids facility, the world’s largest, in Qatar in 2011. South Africa’s Sasol Ltd., the largest producer of motor fuel from coal, announced plans last year to build a $14 billion gas-to-liquids plant in Louisiana.

“While we cannot speak to another company’s plans, we continue to view our proposed GTL facility in Louisiana as a very attractive opportunity as we advance it through the front- end engineering and design phase,” Russell Johnson, a spokesman for Johannesburg-based Sasol, said in an e-mail Thursday.

The economic viability of turning natural gas into fuels depends on the relationship between oil and gas prices. For a gas-to-liquids plant to make money, a barrel of oil has to trade at a ratio of about 16 times the cost of a million British thermal units of natural gas, Sasol Chief Executive Officer David Constable said in an interview last year.

Louisiana had offered Shell a $112 million grant as well as tax incentives for the project, which would have created 740 direct jobs and employed as many as 10,000 construction workers during peak building activity.