That "oil" is more likely migration of the anti-aging/UV protectant micro waxes that are purposely part of the tire's construction.
It is an example of the tire term "blooming", which is the designed feature of a tire to move a minute amount of the anti-aging/UV waxes to the outside of the tire when it is driven for a few miles or when new, just high heat of the air will start the process.
In May, I had new Kuhmo's and wheels installed on the old Bird and drove home a total of 40 miles, temp was around 94 F, and when I pulled in the driveway, the new tires looked like they had been "dressed", however, I knew better as I was with the car and tire installation the whole time. (Store owner is a friend of mine for many years)
If you clean all of this off, and then go out on the interstate and drive at 70 mph for 20 minutes, get out and there will be the "oil" again, as it is supposed.
Removing this with a degreaser does not do the tire any good, removes too much of the protective wax.
Just as allowing a vehicle's tires to set on it for a couple of month in the summer and exposed to sunshine/uv rays without being driven is not good for the tires. The UV's eat up the protective wax and then premature sidewall aging starts (cracking). Which is why I don't have just a car cover for the Bird, due to lack of garage space, but a set of inexpensive Harbor Frieght canvas wheel and tire covers for times like now when it is setting for a couple of weeks.
Which is why the use of petroluem distillate/dimethal silicone dressings (greasy/getto shine/slings off) are so damaging, as both of the two main ingrediants of that type of dressing attack and remove the protective waxes.
Grumpy