He pointed out that crude prices dropped sharply after the report came out, but then came back. However, that only heightened his concern over the way the commodity is running.
"Interestingly, oil prices have rebounded from their lows and some would find this impressive," he wrote Thursday. "We find it an opportunity to mitigate damages done to our long positions and will urge those who are long to exit this morning and rush to the sidelines."
Gartman's advice didn't work out well for the day's trading, with US light, sweet crude advancing more than 1.5 percent in afternoon trading.
But he said he remains concerned that the contango effectbetween the current and out-month contracts has him feeling that the trade is too risky. Big oil companies often take advantage of the difference in contract prices but that can make the trading whippy.
"[The] volatility of this weekly number will continue to confound everyone involved," he wrote. "Trade this number at your own risk; do not trade it on ours."
In a subsequent interview, Gartman said he doesn't know how long his sideline stance will stay in place, as he remains "absolutely agnostic" about oil.
Second Opinion: 'Overpriced'
Earlier in the day, Peter Beutel, energy analyst at Cameron Hanover, told CNBChe thinks oil is overpriced and is only at its current levels because of investors borrowing money at low interest and buying the commodity.
"Someday, and I don't know if it's when we go to slightly higher interest rates, if that's when it occurs...a lot of people have to wake up and say, 'What am I doing long oil at even $70, or even $65, maybe $60, maybe $55?' based on the amount of oil we've got right now," he said.
Beutel said there is 22 percent more crude oil in storage than two years ago—"and we don't have near the kind of demand we had two years ago," when oil reached its record high of $147 a barrel.
He added that he could "make a very good argument" for oil between $30 and $40 a barrel—but doesn't see it going there.