Saudi Arabia has signed a series of multi-billion-dollar deals for international oil companies to develop three giant gas projects in the country.

Eight major companies are involved and the total value of the deals are estimated at $25bn.

They represent the first major foreign investments in the Saudi energy sector since it was nationalized in 1975.

ExxonMobil is to lead the most lucrative project, known as South Ghawar, or Core Venture 1.

As well as the US company, the consortium for the $15bn project will also include Royal Dutch/Shell, British Petroleum and the US company, Phillips.

The Core Venture 2 project on the Red Sea coast is also to be headed by ExxonMobil, together with Occidental and Marathon.

The Shaybah development, or Core Venture 3, is based in Saudi's south-eastern Empty Quarter desert.

It is to be led by Shell taking a 40% stake, with France's TotalFinaElf and Conoco of the US, each expecting a 30% share.

Export boost?

The three natural gas projects are estimated to cover an area the size of Sweden.

The deals - to be carried out in cooperation with state-run Saudi Aramco for up to 30 years - are expected to involve the development of the natural gas fields, along with power plants, pipelines and water desalination projects.

If these international companies are able to help convert Saudi Arabia's domestic utilities from oil to gas dependency, more of the kingdom's crude oil will be available for export.

In addition to the largest oil reserves in the world, Saudi Arabia has proven natural gas reserves of 6.6 trillion cubic metres.