Testimonial evidence in intervening years has shown Saudi assistance was instrumental to America’s policy of forcible regime change and crucial to dismantling Iraq -- leaving the country in the state of corruption and chaos that endures until the present day.
Yet in subsequent years the Saudi’s have largely been absolved of responsibility for their actions in the invasion and occupation of Iraq. This is partly due to the historic relationship between the US and Saudis which has seen western media outlets turn a blind eye to their poor human rights records. Perhaps more importantly, the reputation of SA had taken a battering post-9/11 meaning another highly controversial case was necessary to be kept under wraps in order to maintain the kingdom's crumbling credibility.
Collusion between the 2 countries in the months leading up to the invasion saw the Saudis allow America to double the number of US troops in the kingdom. They also permitted the US to station 350 aircraft, with access to 3 different air bases, from which the US launched attacks, intelligence and reconnaissance flights into Iraq. Elite troops were flown into bases in the NW (‘Ar’ar and Tabuk) enabling the US to launch ground attacks into Iraq from Saudi soil.
The initiation of the invasion of Iraq, routinely cited as the 21st of March 2003, was in fact two days earlier on the 19th of March. US special forces and commandos were launched from bases in Ar'ar in Saudi Arabia, whilst Prince Sultan base was used as the command centre to launch air attacks against Iraq.
Thus the deception continued, with Saudi briefings to the media from senior Saudi officials, such as Crown Prince Abdullah, claiming they were completely opposed to a military occupation of Iraq:
"We do not accept that this war should threaten Iraq's unity or sovereignty or that its resources or internal security should be subjected to a military occupation, and we have let the United States know about our position on this”
In the meantime deals were being agreed to provide invading forces with cheap fuel and promises were made by the Saudis to help stabilise oil prices for OPEC once Iraq had been invaded. Not quite what you'd expect from a country supposedly opposed to “war against our brother Iraq”.
Saudi and US fears of Saddam Hussein, meant the idea of regime change in Iraq became a priority to both combat this perceived threat. The Saudis also envied Iraq’s role as the leading proponent of pan-Arabism in the region, and wanted to take its place at the head of this movement.
Despite seemingly having the foresight to recognise that "If change of regime comes with the destruction of Iraq, then you are solving one problem and creating five more problems”, the Saudis continued to support America's invasion preparations.
Whilst saudi government officials were telling US counterparts they would not allow the US to launch attacks from Saudi, military leaders were part of an ‘unmistakable, albeit secret, connivance’ through which US generals were given assurances that Saudis would open their bases to US forces.
This once again cemented the duplicitous PR campaign undertaken by SA to distance themselves from US aggression against Iraq, enabling the Saudis to maintain an image that was at odds with their actions on the ground and official policy.
The Saudi longstanding security dependence on the US meant that in practice there was no way the Saudis would not kowtow to US demands.
Regardless of the reasons behind Saudi involvement in America's war against Iraq, there is no denying that the role they played was essential.
Sources:

Saudi Arabia's help during war was more extensive, officials say |

Saudis Secretly Provided Extensive U.S. Help During Iraq War |

Saudi Arabia rejects participation in war against Iraq |

A Saudi Prince Tied to Bush Is Sounding Off-Key |

The US-Saudi relationship and the Iraq war |

Saudis warn US over Iraq war |

Iraq: International Attitudes to Operation Iraqi Freedom and Reconstruction - June 2003 |

Iraq: International Attitudes to Operation Iraqi Freedom and Reconstruction - Dec 2003 |