This morning I went to get gas and decided to warm up my engine oil before doing an oil change. When I got home I see on my pass-side door thin black lines of some oily crud. Gobs of it were thankfully either on the front wheel well or on the lower black plastic side moldings, near the front mud flap. (I didn't see any on my tire.) I went to get a paper towel and tried to wipe a small streak off my door panel, but I only made it worse by smearing it. I then tried soaking the towel in car wash soap, still same result, though the blackness of the smear lessen. This substance is oily and sticky. It must have happened as I was driving this morning. I was behind an oil tanker on my way to the freeway. Could it be that? Other than that, perhaps I ran over some oily puddle? My car is white, and this thing is hard to get off. For now, I have left the marks on. I don't want to use dishwashing detergent. Is there something out there I can use that is safe on car paint?

Anyone know what this black oily crud I am talking about? What is it? And how did I get it? (Oil truck in front of me?)