Oil
Oil stains can challenging to get our of carpet, because they spread and stick to the fibers. The best way to extract oil is to spread a thick coat of baking soda across the area where the stain can be seen and leave it there until the sides form a dry crust.
Then, vacuum up the residue. The stain will hopefully be much lighter, or gone altogether. You may have to repeat this process to get the oil stain completely out of the carpet.
