Officials of the United States of America and Nigeria are investigating Ghana’s Saltpond Offshore Producing Company on suspicion that it is being used to tranship and smuggle stolen Nigerian crude to Europe, according to the Wall Street Journal (WSJ), a US-based newspaper.

U.S. officials told WSJ that Washington is probing Saltpond as part of a broader inquiry into how Nigerian oil gets stolen and laundered.

According to the WSJ, Saltpond oil fields appear to be sending lots of crude to Europe, raising questions.

Saltpond platform was inaugurated in 1978 to pump oil from an offshore field. In its heyday, the field, located seven miles off the country's coast, produced more than a million barrels a year. That has dwindled to just over 100,000 barrels over the course of 2013.

But since last August, three tankers picked up more than 470,000 barrels from Saltpond, transporting it to an Italian refinery near the port of Genoa, according to port officials, ship-tracking services and port records, reports the WSJ.

Some U.S. and Nigerian officials suspect Saltpond is one of several destinations that smugglers use to tranship stolen Nigerian crude, effectively laundering it by making it appear to come from a legitimate source outside of Nigeria, says the U.S. newspaper.

The WSJ explained that officials of Saltpond Offshore Producing Company deny wrongdoing, and Nigerian officials say the facility has a legitimate contract with Nigerian authorities to transship oil that the country's law enforcement officials have confiscated. But those volumes are small, according to the Nigerian government, raising questions about the origins of the rest of the oil Saltpond’s platform has loaded onto ships.

WSJ said the Saltpond platform has been a destination for at least one vessel connected to Nigerian oil theft, according to ship-tracking services.

According to the paper, Saltpond has been a frequent port of call for at least one vessel connected with Nigerian oil smuggling.

The ‘Akshay’ is a tanker co-owned by Ajay Bhatia, an Indian national who was sentenced in a Nigerian court in May in absentia to 15 years in jail for oil theft.

The WSJ said the ‘Akshay’ travelled three times between Nigeria and Saltpond in the four months before the ship's seizure by the Nigerian navy for allegedly carrying stolen crude in November 2012, according to shipping tracker service IHS Fairplay.

The newspaper stated that two other vessels partly owned by Mr Bhatia also travel frequently from Nigeria to Saltpond, according to vessel database FleetMon.com and some of the ships' crew members.

WSJ reports that Emmanuel Oware, general manager of Petro-Marine Consult Ltd, based in Tema and which specialises in ship cargo inspections, said that small vessels that have loaded what he called "unofficial" oil in Nigeria's oil-rich Niger Delta frequently come to discharge at Saltpond. There, the Nigerian crude is mixed with Ghanaian oil, he said.

"It comes from Nigeria, but it gets a certificate of Ghana origin," Oware said.

The oil is then transferred to larger tankers, according to Mr Oware, who said he inspected a transhipment at Saltpond last year.

The majority owner of the Saltpond platform, Lushann International Energy Corp., a private company based in Houston, does not dispute that some of the oil it loads onto tankers come from Nigeria.

But Lushann's owner said the company purchases the crude legally from Nigeria's Economic and Financial Crimes Commission (EFCC), the authority with primary responsibility for cracking down on oil smuggling.

The company says the EFCC sells crude that it seizes in its pursuit of oil theft. "The only crude we take from Nigeria…has been seized by the government," said Quincy Sintim, Lushann's owner and president, in a telephone interview. "We have invoices that we pay to EFCC Nigeria."

Mr Sintim said Saltpond's production had never been higher than 200,000 barrels a year since his company took over in 2000, and declined to comment further.

According to WSJ, Jarrett Tenebe, the owner and head of Fenix Impex Nig Ltd, a Nigerian oil-trading firm, said he had been selling confiscated Nigerian crude oil to Saltpond on behalf of the oil ministry, but said the quantities were small.

Dorothy Bassey, head of public affairs at Nigeria's department of petroleum resources—the oil ministry's regulatory body, said Fenix only loaded "about 2,000 barrels" of confiscated crude oil since late 2012. It is unclear how much of that was sold to Saltpond.

Fenix is Saltpond's only provider of EFCC-confiscated crude, according to Mr Sintim.

The provenance of the other oil that made its way to an Italian refinery over the course of the past year, however, is not clear. Three cargoes, listed in shipping documents as "Saltpond blend crude oil," went to Genoa's terminal for delivery to Italy's Iplom SpA refinery, according to shipping and port records and officials.

The WSJ reports that two cargoes, unloaded in August 2013 and February 2014, carried about 340,000 barrels altogether, according to Genoa port officials. The third tanker, unloaded on April of this year, carried 132,000 barrels. Together, that's more than four times the platform's 2013 output of around 100,000 barrels, according to the Ghana government figures.

Giorgio Profumo, Iplom's president, confirmed to WSJ that his refinery had received crude labelled as coming from Saltpond, but said he believed the cargoes were legitimate because they are approved by the Ghana authorities.

Ghana's customs and petroleum regulator did not return an emailed request for comment and could not be reached over the phone, says WSJ.

Asked about the ‘Akshay’ and other vessels co-owned by Mr Bathia, Mr Sintim said he would look into those tankers' activity at Saltpond, but he did not respond when contacted again, WSJ said.

A lawyer for Mr Bhatia declined to comment. Mr Bhatia didn't respond to numerous calls, text messages and emails.

All the activity at Saltpond has ratcheted up scrutiny of the facility—which also includes a storage tanker—and its possible role in the market for stolen Nigerian crude. For years, Western companies operating in Nigeria, like Royal Dutch Shell RDSA.LN -0.37% PLC and Chevron Corp. CVX -0.64%, have lost millions of dollars a month to bandits who tap onshore oil pipelines and siphon off crude.

In recent years, executives and officials estimate that as much as 80% of Nigeria's stolen oil is being shipped out of the country in small tankers. Where it goes, though, has long been a mystery.

"Tankers often will come twice a week to load [stolen oil in Nigeria] and will go abroad," a senior U.S. official familiar with the issue said, referring to international smuggling and not to Saltpond. "But it's extremely difficult to investigate the final destination."