Business & farm

Cap Loss is ($30) in your example, not ($170).  That's because you have other losses being put on Sched E by USO.

If you open up Forms mode, and go to the Form called "K-1 Partner" for USO, you'll see all your entries for the partnership.  At the very bottom of that form, there's a Section C: "Income and Loss Reported on Sched E".  Since this was a final disposition, Column h (Loss K-1) under the non-passive category, should have a number in it.  Let's say its $70.

That $70 is a loss that's going to make its way through Sched E and onto your 1040, line 17.  It will be on line 17 as ($70), reducing your taxable income.  That's the rest of your loss that you're trying to find above.  

In total, your gain loss is the cash that went in and out of your pocket:  $200 (from the sale) + $0 (we'll assume no distributions) - $100 (what you paid).  On your tax forms, that same number is going to show up as a combination of 1099-B, Form 4797 (if you had Ordinary Gain), Sched E (for any losses the partnership passed through), and any other spot the partnership may have reported income or deductions.  It can be complicated to reconcile, but it does work out.