In the introduction to his oak section, Gagne says, "Some kinds of galls can be seen on many species of oak, but it is not known whether they are all made by the same species of gall midge. Further, the damage made by some species has not always been clearly described. For these reasons, the following key will list for most gall midge species only the type host and type locality, even though the galls may be widespread in eastern North America." Clearly, the only sure way to identify a gall like this would be to rear it out and send the adult to Gagne, or someone else who is qualified to identify it. Without having an adult, I think Polystepha globosa is the best place to put these images.

Charley, there is one thing that is worrying me about the ID of this gall, it doesn't in the least look like the only other one in the guide,
see .
The latter, aptly named as Polystepha globosa, is a very small spherical gall on the underside of the leaf. Mine was a blister gall mostly visible on the upperside.
Coincidentally, both pictures were taken at about the same time of the year.

we can't be certain of the species-level ID, but this seemed to me the best place to put the images given the information I have available. I just checked Weld (1) and he lists no cynipid galls that resemble this. Just before the passage in Gagne that I quoted above, he says: "Galls of Polystepha are one-celled spot or blister galls on red and black oaks in eastern North America. Galls are evident in late summer or early fall. . . Galls develop slowly, and the usually orange larvae reach their full size in fall." For P. globosa he states that the gall is "usually" found on the lower side of leaves. I see no reason to doubt that these are Polystepha galls, but you can move them to genus level if you feel better about that. The only other possibility, I think, is that these were cynipid-induced galls that were going to be much larger--oak apples, or something like that--but they were stunted because inquilinous midges took them over. However, the only inquilinous midge species Gagne mentions on oaks are Lasioptera species in galls that don't resemble these ("Tapered, woody swellings on twig, petiole, or midvein, some of them caused by cynipid wasps").

It's possible that more work has been done on these in the past 20 years. You could try contacting Dr. Gagne here. He would probably be interested in examining specimens if you were able to rear adults from these.