A crude oil contango occurred again in January 2009, with arbitrageurs storing millions of barrels in tankers to profit from the contango (see oil-storage trade). But by the summer, that price curve had flattened considerably. The contango exhibited in Crude Oil in 2009 explains the discrepancy between the headline spot price increase (bottoming at $35 and topping $80 in the year) and the various tradeable instruments for Crude Oil (such as rolled contracts or longer-dated futures contracts) showing a much lower price increase.[10] The USO ETF also failed to replicate Crude Oil's spot price performance.
[1] https://en.wikipedia.org/wiki/Contango
EDIT
To add relative context from the link:
A crude oil contango occurred again in January 2009, with arbitrageurs storing millions of barrels in tankers to profit from the contango (see oil-storage trade). But by the summer, that price curve had flattened considerably. The contango exhibited in Crude Oil in 2009 explains the discrepancy between the headline spot price increase (bottoming at $35 and topping $80 in the year) and the various tradeable instruments for Crude Oil (such as rolled contracts or longer-dated futures contracts) showing a much lower price increase.[10] The USO ETF also failed to replicate Crude Oil's spot price performance.