Fahd, who is in his early 80s, has been treated amid relative secrecy at the King Faisal Specialist Hospital in southwest Riyadh since his admission on 27 May.
A medical source who saw the king in recent days said he is on a respirator to help his breathing as he continues to fight pneumonia.
From the outset, his brothers have said Fahd's health is improving and he could be out of hospital within days. Many Saudis remain unconvinced.
"There is a deliberate media blackout on the real state of his health," said Ahmed Otaibi, a 32-year-old owner of a health clinic, adding that the policy might be aimed at avoiding domestic or international problems.
"I just want the king to be well," he said.
The royal family is anxious to give the impression of business as usual in the world's biggest oil exporter, which has been tackling a two-year wave of violence by supporters of Saudi-born Osama bin Laden's al-Qaida network.
"There is a deliberate media blackout on the real state of his health"
Ahmed Otaibi, Saudi citizen
Interior Minister Prince Nayef -Fahd's younger brother - travelled to the United Arab Emirates this week to discuss a border accord, and Foreign Minister Prince Saud al-Faisal flew to Egypt for talks, apparently to show that Fahd's illness has not paralysed affairs of state.
Fahd had a stroke in 1995 and since then day-to-day rule in Saudi Arabia, home to Islam's holiest sites, has passed to another brother, Crown Prince Abd Allah. Diplomats expect a smooth succession when Fahd dies.
Still, the first reports of King Fahd's illness helped drive up world oil prices and pushed Saudi share prices down nearly 5% in a single day.
The usual early summer transfer of Saudi Arabia's royal court from the capital, Riyadh, to the Red Sea city of Jedda has been delayed because of uncertainty surrounding the king.
Saudi Arabian share prices fell
nearly 5% in one day
Diplomats say Fahd's continued hospital confinement, despite first-class medical facilities at his royal palaces, shows the monarch remains gravely ill.
Officials say Fahd was born in 1921 or 1923 - at the time few records were kept in the impoverished desert kingdom his father was still creating before the discovery of oil.
By the time he became king in 1982, Saudi Arabia's oil wealth meant Fahd had inherited one of the world's richest thrones.
His decision in 1990 to allow US troops to be based in his country, the cradle of Islam, was key to the freeing of Kuwait from Iraqi forces. But it fuelled Islamist anger and enraged Bin Laden, whose supporters launched a wave of attacks in Saudi Arabia in 2003, shortly after most US troops were withdrawn.
The Saudi leadership is keeping
business as usual in state affairs
Since his stroke, Fahd has used a wheelchair and has been little more than a royal figurehead.
"We want King Fahd to return to this," said university student Badr Sulais, waving a mobile camera phone bearing a picture of the Saudi monarch, healthy and robust, at a desert camp in the 1980s.