Rob,
Thanks for the response. I do appreciate all the detail. This blocking session is for a Grails/GORM/Hibernate app that doesn't do any external calls (that I know of). All the SQL Text for that SPID during the 10 minutes before the blocking were all just SELECT statements. But as you said, there is no guarantee that those are the only statements that it actually ran. If I see this a lot, I'll get a web developer to help me try to hunt this down. I've heard that JDBC has been known (here, anyway) to occasionally just drop connections and such, so it may not even be an issue in the application code.
Anyway, thanks again for the info.
- Mark