Is the oily liquid from roasting a turkey worth keeping?
Before you use the drippings, taste them. If they taste good on their own, they will be great for gravy. Often, the oil left in the pan after roasting turkey is used to make the roux to thicken gravy to go with that turkey. If it looks like all oil, you can use it as such.

Especially since the turkey was pre-basted, the drippings might be a mixture of oil and juices. Pour the drippings into a clear container so you can see just how much is oil and how much is juice. Scoop off the oil and cook it (and added butter as necessary) on the stove (preferably in the roasting pan) with an equal (roughly) amount of flour. 


  To make a roux gravy, the basic formula is 2 tablespoons fat, 2 tablespoons flour, and 1 cup of liquid to equal 1 cup of gravy.


Quote from about food which meshes with my own experience.

As you cook the flour and oil to a medium brown, try to scrape up any brown bits stuck to the pan. Those are huge flavor bombs. The liquid portion of the drippings poured off can be added with the broth that is the liquid part of the gravy.

The above link leads to more detailed instructions.