Rickie Weeks' Run Scoring

I think that it is pretty universally accepted that when Weeks gets on base, he scores. If only his OBP was higher, he'd be unstoppable. My question is this: What percent of times on base does Weeks score, and how does that compare to the team/league averages? The trick to figuring this out is that not all runs scored are a result of getting on base (HRs), and walks and IBBs must also be taken into account. I suppose an even more useful stat would be the percentage of runs scored when on base with less than 2 outs or with no outs. Any Ideas?