(Bloomberg) -- Oil’s crash below zero last month may have been short-lived -- and confined to the U.S. -- but it helped ensure that at least one producer was paid absolutely nothing for its crude.

Gulf Keystone Petroleum Ltd., which operates the 36,000-barrels-a-day Shaikan field in northern Iraq, invoiced the Kurdish regional government a “nil amount” for what it pumped in April. The London-listed firm said the monthly average price for Dated Brent was less than the discount for its crude. Gulf Keystone sold Shaikan crude at about $21 a barrel below Brent during the month.

It’s unclear whether the company or Iraq’s semi-autonomous Kurdish region ended up footing the bill for the difference, small as it probably was. A spokesman for Gulf Keystone didn’t immediately respond to a request for comment.

Other producers in the Kurdish enclave, including Genel Energy Plc, did get paid last month. Even so, at least a few energy firms operating elsewhere are likely to have met the same fate as Gulf Keystone.

South Sudan’s a possible case in point. The war-torn nation’s Dar Blend and Nile Blend grades of crude often price at a discount to Dated Brent. Operators also have to pay hefty fees to Sudan to transport oil through its territory -- those alone can amount to around $25 a barrel.

The consolation for such companies is that oil’s surge in the past month -- Brent futures are up about 70% to almost $35 a barrel -- means they should get at least something for their efforts in May.

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