A slew of crude imports from Iraq, Angola and other countries has storage tanks in the eastern U.S. Gulf bulging, pressuring physical prices, causing port congestion and delaying deliveries into Louisiana, traders said.

With arrivals into the world’s biggest energy market this month set to top April levels, traders expect the strain on U.S. infrastructure could move inland, further swelling inventories already at record highs.

The glut of domestic crude has kept growing even as futures prices rallied nearly 20 percent in April. Market watchers said the issue in Louisiana could dampen prices ahead.

Shipments have already boosted stockpiles in Louisiana, home to some of the largest U.S. refineries like Marathon Petroleum Corp’s 522,000 barrel per day Garyville refinery and Exxon Mobil Corp’s 502,500-bpd Baton Rouge refinery.

Tanks in the St. James region have as much as 22 million barrels, just 700,000 barrels shy of its record in March, according to Genscape. That is equivalent to around 70 percent of capacity and up from 57 percent, or 17 million barrels, a year ago.

Two shipping sources familiar with operations said the shortage of tank space is causing delays of up to two weeks in offloading crude in Louisiana, including into the Louisiana Offshore Oil Port (LOOP), the largest privately owned crude storage terminal in the United States.

A LOOP spokesman did not address the timing, but called vessel traffic “high” and said the port was trying to offload vessels as “expeditiously as practical” while working closely with shippers on logistics schedules.

“Inventories are still sky high and it hasn’t just evaporated,” said Sandy Fielden, an analyst at RBN Energy. “There are still a lot of issues trying to find storage space even just for operational reasons.”

Storage limits at the U.S. hub of Cushing, Oklahoma, were tested earlier this year. The glut fed worries about supply imbalances as a sell-off pushed oil to 12-year lows.

Physical crude grades are “losing steam quickly”, said one crude trader.

WARNING SIGNS

Gulf Coast refineries went on a buying spree in March as global benchmark Brent’s premium narrowed against the U.S. benchmark, and even briefly fell to a discount.

U.S. imports of West African crude are expected to rise to at least 13.4 million barrels in May, the highest since October 2013, from 13 million in April. A large volume of Iraqi crude is also expected to arrive stateside.

The first warning sign of the crude bottleneck was seen in recent weeks in the opaque physical market, when the light U.S. Gulf Coast benchmark, Light Louisiana Sweet, traded at 88 cents per barrel over the U.S. benchmark for May, its weakest since January. It has since recovered to just under a $2 a barrel premium.

The LLS May/June spread, known as the box, also flipped into a contango for the first time since December, according to two trading sources.

The May/June contango for Mars Sour, the Gulf Coast sour grade, widened to as much as $1 at the end of April from 30-50 cents earlier in the month, dealers said.

The move prompted a large rally for storage futures on the CME Group’s sour contract, with storage trading at a record $1.85 a barrel in recent weeks – the most since the contract started at the end of March 2015.

Still, some traders were skeptical at how quickly oversupply in Louisiana would affect the overall crude market. One trader called the Eastern Gulf area “logistically challenged,” with few pipelines reaching the region, which would have limited direct effects on Cushing.

Crude could move toward the Midwest, however, which then connects to Cushing.

Others pointed to much healthier balances in June, with the LLS box moving back into backwardation. The Mars box also looked a lot healthier, dealers said.