US shale oil rivals Diamondback Energy and Endeavor Energy Resources are close to finalizing a roughly $25 billion cash-and-stock deal that would create an oil and gas company valued at more than $50 billion, sources said on Sunday.

Report informs via Reuters that Diamondback could announce a transaction as soon as Monday that would give its shareholders more than half of the combined companies, the people said, which would become the largest, pure-play oil producer in the Permian shale field.

Reuters in December reported that Endeavor Energy Partners was exploring a sale that could value the largest privately held oil and gas producer in the Permian basin at between $25 billion and $30 billion.

Endeavor and Diamondback did not immediately respond to a request for comment.

The combined company would be the third-largest oil and gas producer in the Permian, the top US oilfield that straddles West Texas and New Mexico. Its oil and gas volumes would be behind Exxon Mobil and Chevron, which have announced recent deals.

"This is a layup in terms of the acreage overlap and fit," said Dan Pickering, chief investment officer of Pickering Energy Partners. The combined company would replace Pioneer Natural Resources, which is being acquired by Exxon, as the top solely Permian producer, he said.

Permian producers are consolidating in a race to lock in future drilling inventory and output from the top US oilfield. The deal is likely to put additional pressure on the remaining firms to combine for greater efficiencies and scale, analysts said.