LONDON—International oil companies working in Iraqi Kurdistan will begin receiving monthly payments from September for the crude-oil they produce and export for the first time since December, the semiautonomous region's government said on Monday.

The development marks the first good news in months for U.K. oil producers like Genel Energy PLC and Gulf Keystone Petroleum Ltd. and Norway's DNO ASA, whose bets on Kurdistan had soured as they pumped around 300,000 barrels a day in the first half of the year without payment for exports. The companies and analysts have said they are owed more than $1 billion.

Their shares soared on Monday. Gulf Keystone rose 27.6%, while DNO was up 26% and Genel rose 11.6%.

The news comes as Iraq is exporting record levels of crude oil in a furious bid to maintain market share during a period of low oil prices and keep its treasurys full for its war against Islamic State, which occupies much of the country.

The Kurdistan Regional Government said it would fund the payments from its controversial direct crude oil sales from Turkey's Mediterranean oil terminal Ceyhan, where Kurdish and northern Iraq oil is sent via pipeline. The KRG is supposed to sell its oil through Iraq's state company but began ramping up its independent sales of oil through Ceyhan after a disagreement over pricing.

The KRG exported an average of around 570,000 barrels a day in June through the pipeline to Ceyhan, it said last month.

Those disagreements, along with an expensive fight with Islamic State, previously had been cited as obstacles to paying the oil companies.

The government said the payments will initially cover Genel, Gulf Keystone and DNO's ongoing expenses, but will increase as exports from the region rise in early 2016.

"The KRG…recognizes the patience of the producing [companies], which, despite receiving hardly any payments for their crude oil production since May 2014, have maintained operations and have continued to invest to support Kurdistan's crude oil export," the KRG's Ministry of Natural Resources said in a statement.

Genel declined to comment. DNO and Gulf Keystone weren't immediately able to comment.

Situated in northeastern Iraq, Kurdistan is a Switzerland-sized region estimated to hold 45 billion barrels of oil. Crucially that oil is onshore and relatively straightforward to access, making it cheaper to develop than more technologically challenging offshore fields elsewhere. It costs Genel about $2 a barrel to pump oil from its Kurdish fields and Gulf Keystone around $5 a barrel.

But to date, the three companies have only received a single payment of $75 million between them at the end of 2014—the first since exports scaled up in late 2013. The December payment didn't fully cover what the companies were owed.

The three companies have been struggling financially and have pulled back on investment in production increases, limping along on sales to the Kurdish domestic market, for which they have been paid.

Gulf Keystone, which was owed $103 million at the end of the first quarter, has seen its share price crash and its bonds are trading well below their face value. The company is talking to prospective buyers about a sale of the entire company or a partial sale of its assets, which include the giant Shaikan oil field in Kurdistan.

Genel, which is headed by Tony Hayward, the former chief executive officer of BP, was owed $378 million at the end of June, but has been partly shielded thanks to a cash pile it built up during a bond issue last year that raised $500 million. However, the company has had to cut capital spending and deferred drilling.

DNO, which analysts say is owed around $600 million, swung to a net loss in the first quarter and said further investment to maintain output in Kurdistan would depend on export payments.

Kjetil Malkenes Hovland contributed to this article

Write to Selina Williams at selina.williams@wsj.com

Subscribe to WSJ: http://online.wsj.com?mod=djnwires