Some of the more popular products using this strategy, like United States Oil ( USO ) and United States Natural Gas ( UNG ), substantially underperformed their spot commodities due to a persistent and outsized negative roll yield. For instance, UNG lost 12% of its value during the summer of 2007 while the spot commodity actually gained 1%. As the Fed executed extremely loose monetary policy, hoping to prevent a deflationary spiral through the direct injection of capital to the economy, inflationary fears began to surface.