Kuwait was drilling sideways aka “slant drilling” at its border with Iraq to illegally access Iraqi oil, with the blessing of the US of course. That’s the reason for Iraq attacking Kuwait.

Charles Jannuzi
Associate Professor (1994-present)
It was quite likely true. Iraq had some very legitimate claims against Kuwait and Saudi Arabia. That didn’t justify invasion. But what did Saudi Arabia and the Gulf States think Iraq was going to do? Drown in debt? Dismantle its army?
Iraq and Kuwait were ‘sharing’ a known oil field (which on the surface mostly fell in Iraqi territory), and Iraq thought that Kuwait was using directional drilling to take more than its share. Iraq and Kuwait had never negotiated a deal for how to share the field, since Iraq rightly felt that Kuwait wasn’t entitled to any—that the border had been drawn to give them some of the oil.
Kuwait actually didn’t dispute the claim. It instead countered that Iraq had exaggerated the amount (Iraq accused Kuwait of stealing 300,000 - 350,000 barrels a day).
Even if Kuwait wasn’t using slant drilling to take oil out of clearly marked Iraqi territory, it was using it to take more out of a shared field, far exceeding any amount it was entitled to for having a bit of the field fall in Kuwait.
It was also over-producing oil and driving down the price, in large part due to the huge amounts of oil it was sucking out of the Ramaila field. Iraq had a pretty good idea of just how much oil Kuwait could produce, so that is why it figured out that Kuwait was sneaking more oil out of the shared field using directional/horizontal drilling that was not visible from the activities just across the border that could be observed.
The cause of the dispute: Kuwait using the fact that a small part of the huge Rumalia oil field falls inside Kuwait in order to siphon huge amounts of oil out of it.
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