Burns Slant Drilling Co. was the company owned by Charles Montgomery Burns to mine the oil found underneath of Springfield Elementary School to ensure Mr. Burns reaps the profits and rights to the oil. Besides ruining Springfield Elementary School's financial prosperity to such an extent that it was left in an even worse financial situation (bad enough that Seymour Skinner was forced to not only deny Tito Puente a teaching position due to having to remove the music department, but also fire Groundskeeper Willie as well, thus resulting in the two of them as well as Skinner himself holding a grudge against Burns, the latter two to murderous levels), the company was directly responsible for the shutdown of Moe's Tavern next door, as Moe and the various barflies, including Barney, were forced out of the premises due to the toxic fumes being emitted from the drilling operation, which resulted in at the very least Moe and Barney gaining enough of a grudge against Mr. Burns as to want him dead; the destruction of Bart's treehouse due to the oil spray proceeding hitting the tree house via the trajectory, which resulted in Bart Simpson and especially his pet dog and friend Santa's Little Helper experiencing injuries (much more severe in the case of the latter) due to being in the tree house at the time, infuriating Bart enough regarding the latter's injuries that he attempted to rush at Mr. Burns in fury when the latter showed up at a town hall meeting and would have beat him up in retribution had Mr. Burns not unveiled a gun; and the forced closure of Springfield Retirement Castle due to the foundation being weakened from the draining of oil causing the ground beneath the retirement home to become unstable and nearly cause it to collapse, thus earning Burns' ire from the retirement home folks (in particular Jasper Beardly and Abraham Simpson II), and was indirectly responsible for Waylon Smithers, Jr.'s firing, as the latter was already disgusted with his former employer for the aforementioned actions (barring the bit about Bart Simpson's tree house being destroyed) and already attempted to advise him against stealing the school's oil before expressing that Burns' next plan, the Sun Blocker, was going way too far and spoke out against it, which likewise also resulted in Smithers getting a murderous grudge against his former boss.
After Mr. Burns was shot, it is unknown it the Slant oil rig was destroyed, or if the school was able to regain its oil.