From Wikipedia

The First Gulf War

Part Three

The rapid success of the Iraqi army had brought it within easy striking distance of the Hama oil fields, one of Saudi Arabia’s largest oil fields. Iraqi control of these fields as well as Kuwait and Iraqi reserves would have given it control of the majority of the world's reserves. The Iraqi armoured divisions would have encountered the same difficulties that Saudi forces faced defending the oil fields, namely traversing large distances across inhospitable desert. This would have been exacerbated by intense bombing by the Saudi Air Force, by far the most well-equipped arm of the Saudi military.

Iraq had a number of grievances with Saudi Arabia. The Saudis had lent Iraq some 26 billion dollars to prosecute its invasion of Iran, as they feared the influence of mainly Shia Iran's Islamic revolution on its own Shia minority (most of the Saudi oil fields are in territory populated by Shias). The long desert border was also ill-defined. Soon after his conquest of Kuwait, President Hussein began verbally attacking the Saudi kingdom. He argued that the US-supported Saudi state was an illegitimate and unworthy guardian of the holy cities of Mecca and Medina. President Hussein combined the language of the Islamist groups that had recently fought in Afghanistan with the rhetoric Iran had long used to attack the Saudis.