Oil and gas producer Cimarex Energy Co agreed to buy smaller rival Resolute Energy Corp for $1.6 billion including debt, adding more assets in the shale-rich Permian Basin for a premium of roughly 15 per cent.

However, Resolute’s largest shareholder - Kimmeridge Energy Management Co - said it was dissatisfied with the sale price, highlighting the difficulties US energy mergers are facing due to crude price volatility.

Several deals involving the Permian, the heart of the US shale boom, have been announced this year as producers seek combinations to boost scale, allowing them to take advantage of better drilling technology and negotiate better terms with services firms.

Analysts at investment bank Tudor, Pickering and Holt said Resolute’s acreage in the Delaware part of the Permian sits directly adjacent to Cimarex’s, meaning these benefits should be easier to accrue.

The slump in crude prices in recent weeks - WTI has dropped around 25 per cent since the start of October - has made dealmaking more tricky as this volatility affected their stock prices.

Denbury Resources’ shares fell 25 per cent in the week after announcing on October 28 it would buy Penn Virginia in a $1.7 billion cash-and-stock transaction. The seller’s third-largest shareholder said last week it would vote against the deal.