May 31(Reuters) - Cash-rich Exxon Mobil and Chevron are bolstering their oil and gas drilling inventory with multi-billion-dollar takeovers as they bet on resilient demand for years to come.

The consolidation wave sweeping through the U.S. energy sector that spurred deals worth $250 billion in 2023 shows no signs of slowing as companies rush to deploy their cash hoard from higher oil prices into building even bigger reserves through acquisitions.

Earlier this month, Exxon closed its $60 billion purchase of Pioneer Natural after receiving a go-ahead from U.S. regulators.

The deal would increase Exxon's total production to more than 5 million barrels of oil equivalent per day (boepd) by 2027, making it the biggest producer in the Permian, the largest and most highly valued U.S. oilfield.

Meanwhile, Hess shareholders last week approved the company's proposed $53 billion takeover by Chevron, which will get a foothold in rival Exxon's massive Guyana discoveries and see its production rise to more than 4 million boepd by 2027.

Oil-rich Guyana's lucrative offshore fields are expected to hold more than 11 billion barrels of oil and gas resources.

Exxon currently holds a 45% stake in Stabroek block in Guyana, with Hess and China's CNOOC Ltd as its minority partners.

The approval by Hess's shareholders clears one hurdle, but the merger still needs regulatory approval and must face a lengthy arbitration battle against Exxon.

Chevron, Exxon and other U.S. oil companies have booked soaring profits from strong energy prices since Russia invaded Ukraine.

Although their earnings are down from the bonanza year of 2022, they are still at strong levels.

At the end of 2023, Exxon had $31.54 billion in cash and cash equivalents, while Chevron held $8.18 billion.

Shares of Exxon and Chevron have risen 14% and 6% respectively, so far this year, compared with nearly an 8% rise in the S&P 500 energy sector.

(Reporting by Arunima Kumar, Tanay Dhumal and Sourasis Bose in Bengaluru; Editing by Anil D'Silva)