WTI and Brent crude oil futures on Monday both fell to their lowest levels in nearly five years. Amid contango, more tanker owners will hold off on transporting oil and store it instead, Gartman said.
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Prolonged storage in tankers emerged as a trend in 2008, and buying tankers hasn't proved as appealing since, he said. If contango continues, bets on companies holding oil in tankers—rather than transporting it for immediate sale—will continue to rise, he said.
"I think that what we see right now is going to get even further out," Gartman said. "More people are going to do more buying of tankers."
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Though tankers and storage look compelling now, some data show oil may be nearing a bottom, he said. In recent days, WTI crude has started to gain relative to Brent, which could signal most of the "bearish run" in oil has run its course, Gartman noted.
If low oil prices persist, they will prove "hugely beneficial" to the American economy, he added.