USO's legal structure is that of a partnership. that's why you got a k-1. so you need to report the k-1 info on your tax return. in addition, the 1099-B shows only your original tax basis (what you paid to purchase it in the section - cost not reported to IRS section of 1099-B (type B or D depending on holding period) with the K-1 you should have received a sales schedule which will allow you to compute your correct tax basis which then should be substituted for what's on the broker's statement.
the 1099-B shows only your original tax basis - the reason for this is the broker receives no updates as to items affecting tax basis such as the income/loss and distributions all of which affect your tax basis
