SPECULATION over the declining health of King Fahd of Saudi Arabia continued to capture the attention and to raise the concerns of many political and economic quarters in and outside of the Middle East. Despite assurances offered by senior Saudi officials that the hospitalisation of the Saudi monarch was only for "check-up purposes" and that the king is in a stable and even improving condition, rumours suggesting otherwise have been on the rise. According to Saudi Crown Prince Abdullah, "the medical tests the king underwent prove that his condition is stable and reassuring." Similar statements have been regularly made by other members -- representing other wings -- of the 1,500-member Saudi Royal family. "They say it is only pneumonia that he is recovering from. I am not so sure because Saudi opposition sources suggest otherwise," commented one Cairo-based Arab diplomat. The ailing Fahd has been in power since 13 June 1982. During his rule, Fahd strengthened the kingdom's ties with other Arab states and held a special alliance with the late Syrian president Hafez Al-Assad and Egyptian President Hosni Mubarak. Fahd kept cordial ties with the United States until the Iraqi invasion of Kuwait in 1990. Threats made by toppled Iraqi President Saddam Hussein to invade the Saudi Kingdom prompted Fahd to call on former US President Bush to deploy troops and military assistance. In 1994 Fahd suffered a serious stroke that diminished his capacity for direct rule. Crown Prince Abdullah, a septuagenarian, has been the effective ruler of the kingdom since. Abdullah has largely maintained Fahd's policies but has developed a closer alliance with the US. Saudi Arabia hosted a considerable number of US troops during the first Gulf War against Iraq -- Desert Storm -- in 1991. Most of these troops were reported to have been pulled out in accordance with a 2003 agreement between the Saudis and the Americans in the wake of growing militant activities by Islamist groups who oppose the royal family over its style of rule and its close association with the US. Concerned Saudis have been closely following health updates on the status of the king. Instability in the kingdom would have global repercussions due to Saudi Arabia's strategic importance as the nation with the world's largest oil reserves. The Saudi stock market tumbled five per cent earlier in the week amid reports of Fahd's deteriorating health. Fahd's hospitalisation also pushed crude oil futures to near $52 a barrel.