Saudi Arabia has been described as the world "mother lode" of oil and gas reserves. Estimates for 1990 placed total oil reserves of the kingdom at 261 billion barrels. Saudi Aramco controlled all the reserves within the country's borders with the exception of reserves in the Divided Zone, which were controlled by Getty Oil Company and the Arabian Oil Company. Total oil reserves have risen steadily since oil was discovered in 1938. During the 1970s and 1980s, estimates of total oil reserves grew by nearly 91 percent from 137 billion barrels in 1972 (see table 6, Appendix). The comprehensive reassessment of existing reserves boosted Saudi Arabia's share of world reserves to 25.8 percent. At 1992 production levels, these oil reserves would allow oil production for almost eight-four years.

Until the mid-1980s, all the oil that had been discovered had been found in the Eastern Province. Aramco had found forty-seven oil fields, including some during the 1970s in the Rub al Khali. The world's largest oil field, Al Ghawar, located in the Al Ahsa region of the Eastern Province, is 250 kilometers long and 35 kilometers wide at its greatest extent. The field is so vast that names have been given to separate subsections such as Ain Dar, Shadqam, Al Hawiyah, Al Uthmaniyah, and Harad. Discovered in 1948, the field began output in 1951. By 1990 Al Ghawar had 219 flowing wells. Saudi Arabia also possessed the world's largest offshore field, As Saffaniyah, located in the gulf near Kuwait and the Divided Zone. As Saffaniyah was discovered in 1951, began output in 1957, and by 1990 had 223 flowing wells. Of the four fields discovered before Al Ghawar--Ad Dammam, Abu Hadriyah, Abqaiq (also seen as Buqayq), and Al Qatif--only Abqaiq and Al Qatif were still producing in 1990. Abqaiq had forty-seven flowing wells. The major producing fields discovered after Al Ghawar, mainly in the 1960s and early 1970s, are offshore and include Manifah, Abu Safah, Al Barri, Az Zuluf, Al Marjan, and Al Khafji in the Divided Zone (see fig. 6). Saudi Arabia had a total of 789 flowing wells during 1990, up from 555 producing wells in 1983.

Figure 6. Major Oil Fields, 1992

The quality of crude oil flowing from these wells is based on density (measured by gravity standards established by the American Petroleum Institute--API) and the amount of sulfur and wax it contains. Light crude oil is generally more desirable and commands a higher price because it yields more high-value products such as gasoline and jet fuel. Several Saudi fields, including those in the Divided Zone, contain heavier grades by international standards. Al Ghawar field produces crude ranging from API gravity 33 degrees to 40 degrees, which is considered light crude oil in the kingdom but is generally heavier than most international light crude oils. As Saffaniyah produces heavy crude oil with API gravity rangina46 ing from 27 degrees to 32 degrees.

The historical production pattern until the early 1980s contained greater proportions of light and very light crude oils. By the mid-1980s, government policy sought to adjust output between heavy and light crude oils to reflect actual users of each, so that the kingdom would not exhaust its supply of light crude oils. Estimates for 1991 showed that this balance was not achieved, however Extra Light (from Al Barri field) and Arab Light (crudes from Abqaiq, Al Ghawar, Abu Hadriyah, Al Qatif, and others) recorded production levels close to 70 percent of total output of 8.2 million bpd, whereas Arab Medium (from Az Zuluf, Al Marjan, Al Kharsaniyah, and other fields) and Arab Heavy (from As Saffaniyah, Manifah, and other fields) production levels approached 11 percent and 19 percent, respectively. In the early 1990s, the consensus was that after capacity was expanded, the split between light and heavy grades would shift to 10 percent more heavy crude oils, despite recent discoveries of very light grades south of Riyadh. During the 1980s, technological developments in refining narrowed the differentials between light and heavy crudes. Therefore, the traditional price disadvantage that the Saudis faced was steadily being erased because of the more sophisticated refineries being brought on line.

Saudi crude oils also contain high sulfur levels. Crude from Al Ghawar has sulfur content ranging from about 1.9 percent to close to 2.2 percent by weight, which is generally considered high. As Saffaniyah crude's sulfur content is even higher at above 2.9 percent by weight. Sulfur compounds are undesirable, often contaminating crude oils and corroding processing facilities.

Data as of December 1992