Kosmos Energy has agreed to acquire Deep Gulf Energy (DGE) from its private equity owner for $1.23 billion, according to a bourse filing on Monday, expanding the deepwater oil and gas firm's operations into the Gulf of Mexico.

Dallas-based Kosmos, which currently operates in Africa and South America, will pay $925 million in cash and $300 million in Kosmos common stock to acquire DGE, with the transaction expected to close towards the end of the third quarter.

Acquiring DGE's business will increase Kosmos' production by more than 50 percent to 70,000 barrels of oil equivalent per day (boed) from around 45,000 boed now, with the company's estimated reserves rising 40 percent to around 280 million barrels of oil equivalent, the statement said.

"The best deepwater assets can compete with the best of shale, and now is a good time to enter the Gulf of Mexico," Andrew Inglis, chairman and chief executive officer of Kosmos, said in the statement.

Speaking with Reuters, Inglis said the exit in recent years of a number of exploration and production companies from the Gulf of Mexico to invest more in onshore shale projects had created a space in the market for Kosmos to exploit.

It had been able to secure high quality assets without the level of competition that energy firms might experience in other places, he said.

In the London Stock Exchange statement, Kosmos noted the DGE acquisition would be "immediately accretive" to the company and the "significant free cash flow" that the assets would help generate would allow it to pay a dividend to shareholders starting in the first quarter of 2019.

DGE had been backed by energy-focused private equity firm First Reserve since 2005, according to the company's website.

Evercore and Goldman Sachs acted as financial advisers to Kosmos, according to the bourse statement.

(Reporting by David French; editing by Richard Pullin)