By John Spence
BOSTON (MarketWatch) -- U.S. Oil Fund (USO 34.26, -0.48, -1.38%) , a $1.8 billion exchange-traded fund that tracks crude-oil futures, slipped 1.2% early Thursday and was on track for its third straight day of losses. The ETF is off more than 5% so far this week as renewed economic jitters have hit oil prices. It is down 12.6% year to date, according to FactSet Research.
