"It'll be some while. They're not going to come online tomorrow. They're not going to come online next week," he said. "But the market believes and understands, and I think rightfully expects that by the turn of the year we're going to have Iranian crude oil coming back to the market."
(Read more: Iran deal unlikely to help much at the gas pump)
Contango occurs when futures prices for a commodity are greater than the current spot price.
(Read more: Contango: CNBC Explains)
"Prices have been under pressure," Gartman said. "Prices may well continue to be under pressure for some while going into the future."
Crude oil prices could test $85 per barrel levels, he added.
"There's a gob of $110 crude oil out there," Gartman said. "There's probably a good deal less $80 crude."
(Read more: Keep buying stocks at all-time highs: US Trust)
Gasoline prices at the pump could also be lower by the end of 2013, he said.
"I bet we take RBOB under $2.50," he said. "I bet we take the public's gas at the pump under $2.75 gas relatively easily after the turn of the year."