USO delivers its exposure to oil using near-term futures. USO gets exposure to oil using derivatives, like several oil ETPs. The fund predominately holds near-month-futures contracts on WTI, rolling into future contracts every month. This method is particularly sensitive to short-term changes in spot prices. USO held front month contracts until April 17, 2020, at which time following leeway in the prospectus, USO changed the exposure from holding specifically front-month contracts to holding predominantly front-month contracts, 30% next month and 15% contracts with further expiry. USO is structured as a commodities pool, so expect a K-1 at tax time. Long-term holders will be taxed on any gains even if they didn't sell shares.
Per-holder 13F data isn't yet ingested for ETFs — coming with the next data layer expansion.