Welcome to HealingWell!
I really wouldn't worry too much about
the "oil" you are passing unless it is happening a lot (longer than 3-5 days). Sometimes our body has a difficult time digesting fat. Are you seeing the oil with every BM, or just randomly? Are you in pain? Do you bleed? Again, if this keeps up you check with your doc. A cause for "oily" BM's is malabsorbtion. Your doc should be able to check your fat absorbtion by doing a stool test (fecal fat test). Or, another reason could be chronic pancreatis (CP). CP can be diagnosed via a blood test.
For now maybe you could stay away from fatty foods and see what happens... ?
Co-Moderator for the IBS Forum