Exxon Mobil Corp has agreed to sell its majority stakes in a Hong Kong utility and a power storage firm for a combined $3.4 billion, helping the US oil major raise funds to plough back into its core operations, Reuters reported Tuesday.

Many integrated global oil companies have struggled to boost production, spending heavily on new projects in recent years. In the first nine months of this year, Exxon, the world's biggest oil firm by market value, spent $33 billion.

They are also keen to put cash in the pockets of investors through asset sales, share buybacks or dividends as analysts grumble about lagging stock prices.

Under the deal, CLP Holdings will assume control of Castle Peak Co Ltd, one of Hong Kong's main electricity providers, lifting its stake to 70 percent by buying half of Exxon's holding for HK$12 billion ($1.6 billion).

State-owned China Southern Grid (CSG) will buy the other 30 percent held by Exxon but it did not disclose financial terms. A person close to the transaction told Reuters CSG will also pay HK$12 billion.

CLP, which has been providing electricity to Hong Kong for over 100 years, said the deal will help it better manage and coordinate its Hong Kong power generation and distribution business.

It also plans to buy Exxon's 51 percent stake in Hong Kong Pumped Storage Development Co for HK$2 billion.