When a blue ship with the phrase “SHALE GAS FOR MANUFACTURING” painted on its hull docks at Pennsylvania’s Marcus Hook terminal later this year, it will open a new phase in world energy markets.

The vessel and its twin were built to ferry a hydrocarbon called ethane from the shale basins of the US to industrial plants in Norway and Scotland. Theirs will be the first voyages in a nascent seaborne market for ethane, a petrochemical building block for plastic bags, antifreeze and other goods.

Until now trading in ethane has been hemmed in by the continents where it is produced. The substance’s -90C boiling point makes it costly to condense into the liquid state that is required to carry it by ship.

But US supply of ethane, which comes out of natural gas wells, has doubled and prices have plunged 60 per cent from five years ago to $0.19 per gallon. Shale gas producers are stuffing some unwanted ethane into natural gas pipelines to be burnt, a process called rejection. Sensing an opportunity, US energy companies and European and Asian petrochemicals makers have joined forces to build pipelines, tanks, giant refrigerators and specialised tankers to move surplus ethane overseas.

“When you have a hydrocarbon that is priced too cheap, people figure out how to take advantage of that price,” says Jim Teague, chief operating officer of Enterprise Products Partners, which is building an ethane export terminal near Houston.

The ventures are the latest example of how the US is flexing its muscle as a supplier in global energy markets. The country is on the cusp of large-scale exports of liquefied natural gas, its oil refineries are sending out millions of barrels of fuel each day and Congress is debating whether to abolish 40-year-old restrictions on crude oil exports.

US ethane exports were zero as recently as 2013. Late that year, some began to flow north by pipeline to Canada. This autumn, ethane loaded at Marcus Hook is expected to arrive at a “cracker” plant the chemical company Ineos operates in Norway, with subsequent shipments to Scotland. By 2017 US ethane exports will top 300,000 barrels per day, Bentek Energy forecasts.

The burgeoning trade has helped revive troubled industrial sites on both sides of the Atlantic. Marcus Hook, built as an oil refinery, stopped processing crude in 2012 at a cost of 500 jobs. Now, 150 people work there again after owner Sunoco Logistics completed the first of two Mariner East pipeline projects to bring propane, ethane and other natural gas liquids from inland shale regions to be processed, chilled and shipped to customers including Ineos.

Ineos’s ethane crackers in Norway and the UK were in the past supplied from the North Sea. Ineos threatened to close Grangemouth, Scotland’s largest industrial complex, in 2013 over a dispute with labour unions and dwindling North Sea supplies of ethane. The company tried alternatives such as propane without much success. “It was like trying to run your petrol engine on diesel,” says Tom Crotty, Ineos director of corporate affairs.

The company has spent €600m improving its sites in Scotland and Norway to take US ethane, adding two import terminals with towering tanks. In Scotland, Ineos also received a £9m grant from the Scottish government and loan guarantees from the UK government. In time, eight ships will shuttle ethane from the US to Europe, most of it locked up in 15-year supply deals.

In Houston, the Enterprise terminal will be able to export 200,000 b/d of ethane. Asked why the project makes sense now, Mr Teague says: “One word: shale.”

In Panama, energy investment group Gator Partners is planning a 400MW ethane-fuelled power plant mounted on barges that would consume 20,000 b/d of US ethane likely to be shipped from Marcus Hook, according to people familiar with the project.

The growth of the ethane trade will be guided in part by the future direction of oil prices. Ethane is an alternative to naphtha, derived from oil. If oil keeps falling — Brent was about $50 a barrel early on Thursday — ethane will no longer be a bargain and future projects could be mothballed.

“It depends on your view of the natural gas-to-crude relationship. If that relationship gets back to being as wide as it was earlier, then that enhances the potential of a much larger market being developed,” says Mr Teague.

Much also depends on how much ethane is consumed within the US. Sixteen new crackers are in various stages of development in the country, according to Bentek Energy. If all are built, less ethane will be available to the world market.