A four-decade-old U.S. ban on crude exports should remain until a “saturation” point when domestic refining capacity becomes insufficient to absorb increased oil production, according to Goldman Sachs Group Inc.

Maintaining the statutory curb on shipments overseas will deliver the “highest value” to the U.S. economy, the bank said in an e-mailed report. At current extraction costs, the export ban may start to weigh on U.S. output growth in coming years, it predicted.

Rising production from shale formations has allowed the U.S., the world’s biggest oil consumer, to import less crude, fueling speculation that the curb on exports could be lifted.

A 1975 federal law bans most shipments overseas, with only deliveries of refined products including gasoline and diesel allowed. Supporters of the ban say keeping U.S.-produced oil at home helps reduce fuel prices for industry and consumers.

“Keeping the ban in place would be the optimal decision until saturation is reached to maximize the contribution of the refining sector,” said Damien Courvalin, a Goldman analyst in New York. “Once saturation is reached, it would then be optimal to lift the ban as value added from higher production outperforms value added from the refining sectors.”

Uncertainty over the future of the ban is probably delaying investment in U.S. refining capacity, according to Goldman. Oil companies are seeking ways around it by using simple, one-step plants capable of turning crude into products for exports. BP Plc signed on to take at least 80 percent of the capacity of a new $360 million mini-refinery in Houston that will process just enough to escape the restrictions.

IHS Inc. last month said the ban should be lifted because the U.S. will benefit from higher oil production and reduced gasoline prices. The nation may save an average of $67 billion a year from its import bill in 2016 and add 964,000 jobs by 2018, according to the Colorado-based consultant.