Since leather is such a temperamental material, removing stains requires a bit more strategy than on other fabrics. Oil stains are particularly harder to remove. Depending on the size of the stain, you may be able to remove it on your own without having to talk to a leather professional. Larger stains may require professional help. If the stain is small however, it is a quick and simple fix with the right materials.
Blot up any excess oil with a soft, clean dry cloth.
Lay the jacket flat so that the oil stain is exposed.
Sprinkle baby powder or cornstarch on the stain.
Leave the baby powder or cornstarch on the jacket overnight to draw the oil out of the leather and absorb it.
Use the attachment from the vacuum cleaner to remove the powder or cornstarch in the morning.
Do not attempt to use water on the stain as this will make it worse. If the stain will not come out, then you will need to contact a leather professional to fix it.