Equinor, Shell and Exxon Mobil have reached an agreement with the Tanzanian government to develop a liquefied natural gas (LNG) export terminal, the head of Equinor Tanzania said on Friday.

The agreement is an important milestone for the long-delayed project to unlock Tanzania's vast but remote offshore gas resources, which the companies involved have said is expected to cost tens of billions of dollars.

Tanzania to lead Southern and Eastern Africa's largest LNG energy project valued at $42 billion

Friday's agreement includes the key elements of a host government and production sharing agreement, and is subject to legal reviews and quality assurance ahead of a planned signing in the coming weeks.

"This agreement paves the way for a series of steps that must be completed to realize this fantastic LNG opportunity for the country and the world," said Equinor's country director, Unni Fjaer, in a statement.

"The final investment decision on the Tanzania LNG project has not yet been made. Pavilion Energy, Medco Energi and Tanzania's national oil company, TPDC, were also involved in the deal," said Equinor.

The next steps towards the realization of the project involve a period of detailed engineering design work, said Shell's president in Tanzania, Jared Kuehl, in a separate statement published on Linkedin.

Equinor and Shell are joint operators of the development, while Exxon, Pavilion Energy, Medco Energi and Tanzania's national oil company TPDC are partners in the project.

Last June, the parties involved signed a framework agreement to bring the start of construction of the project closer.

In 2014, Tanzania said that developing the project could cost 30 billion dollars, but analysts have said that cost inflation in recent years could add billions more to the investment.

Shell operates Tanzania's Block 1 and Block 4, which hold an estimated 16 billion cubic feet of recoverable gas.

Norwegian oil and gas producer Equinor is exploring Block 2, in which Exxon Mobil has a stake and which is estimated to contain more than 20 billion cubic feet of gas.