Saudi Aramco agreed to sell a 49% stake in its natural-gas pipeline business to a consortium led by BlackRock Inc. and Saudi-backed Hassana Investment Co. for $15.5 billion—the state-owned oil giant’s latest move to pull cash out of its vast energy infrastructure.

The deal follows a pattern used when Aramco agreed to sell a similar sized stake in its oil pipeline network in April for $12.4 billion to a group led by EIG Global Energy Partners. Aramco, officially called the Saudi Arabian Oil Co., said Monday it had formed a...

Saudi Aramco agreed to sell a 49% stake in its natural-gas pipeline business to a consortium led by BlackRock Inc. and Saudi-backed Hassana Investment Co. for $15.5 billion—the state-owned oil giant’s latest move to pull cash out of its vast energy infrastructure.

The deal follows a pattern used when Aramco agreed to sell a similar sized stake in its oil pipeline network in April for $12.4 billion to a group led by EIG Global Energy Partners. Aramco, officially called the Saudi Arabian Oil Co. , said Monday it had formed a new subsidiary, Aramco Gas Pipelines Co., that will lease usage rights in Aramco’s gas-pipelines network. It agreed to sell 49% of the new company to the consortium led by BlackRock unit BlackRock Real Assets and Hassana. Hassana is the asset-management arm of Saudi Arabia’s General Organization for Social Insurance.

Aramco will retain 51% of the company. Aramco will then lease usage rights back from the new company, paying a tariff for gas products piped through the network over the next 20 years. The network involves domestic infrastructure in Saudi Arabia.

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The move follows a series of steps Saudi Arabia has taken to raise cash from its oil assets over recent years. With the ascension of Crown Prince Mohammed bin Salman, the kingdom has been more willing to lure foreign investors and cede some ownership of its oil infrastructure in exchange for funds.

Over several years, Prince Mohammed promoted an international listing of Aramco shares, before ultimately deciding on a local listing of a very small slice of the company. The Saudi government retains a 98% stake.

The oil-pipeline deal in April was another move that, only a few years ago, would have seemed unimaginable for a petrostate that had long considered its oil reserves and related infrastructure strategic assets.

As part of Aramco’s stock-market listing, it agreed to a sizable dividend—$75 billion a year. Aramco is also investing in a multibillion-dollar natural-gas project at its Jafurah field and has promised to expand oil production capacity.

Prince Mohammed has flirted with other cash-raising exercises. In April, he said that Saudi Arabia was talking with unnamed foreign investors about selling stakes in Aramco, with options that include a 1% acquisition by a leading global energy company. 

Despite efforts to diversify the economy away from oil, Aramco remains Saudi Arabia’s main source of revenue, with most of its $75 billion dividend filling state coffers. Aramco had to turn to the debt market last year to help fund the dividend after its earnings plunged with the onset of the coronavirus pandemic. That pressure has eased after oil prices have turned higher.

Write to Summer Said at summer.said@wsj.com