A landmark $25bn (�16.1bn) gas deal between Saudi Arabia and western energy firms is reportedly facing yet more delays.

The deal represents the first major foreign investment in the Saudi energy sector since it was nationalized in 1975.

Firms involved

Exxon Mobil Shell BP TotalFinaElf Occidental Philips Conoco Marathon

But the conditions of the agreement have been fought over since it was first agreed in June 2001.

Saudi Arabia has reportedly put last-ditch concessions on the table in the hope of averting the collapse of year-long negotiations.

But the western firms are now thought to be unable to meet an October deadline, saying they need more time to examine Saudi's final offer.

One local newspaper report suggested that firms would be given an extra month's leeway.

Political embarrassment

Despite the difficult negotiations, the Saudi Foreign Minister has repeatedly stressed his determination to press ahead with the liberalisation of the energy sector "under all circumstances".

Unnamed sources and press speculation have repeatedly suggested that the deal is on the verge of failure.

Prince Saud: determined to press on with liberalisation

Such a failure would be an acute embarrassment to both the foreign minister Prince Saud al-Faisal and Prince Abdullah who were keen advocates of the deal.

Prince Saud, seen as a moderniser, was one of the driving forces behind the initiative and successfully faced down the reluctance of national energy company Saudi Aramco to allow foreign investment in gas exploration and production.

Chief executives of both Exxon Mobil and Shell have already held talks with Crown Prince Abdullah on the matter.

The firms are thought to be unhappy with high taxes and the amount of access given to the prized gas reserves.

Saudi sources have suggested that the projects will be re-offered for fresh bids if there is no agreement with the parties now involved.

Rich resources

The deal is a series of interlinked contracts worth about $25bn with eight major firms to develop gas fields the size of Sweden.

The projects - to be carried out in co-operation with state-run Saudi Aramco for up to 30 years - are also expected to involve the development of power plants, pipelines and water desalination projects.

Saudi Arabia hopes the projects will help convert the country's domestic utilities from oil to gas dependency, freeing up more of the country's crude oil output for export.

In addition to the largest oil reserves in the world, Saudi Arabia boasts the world's fourth biggest gas reserves.