Oil investors may be getting ahead of themselves, betting on an overly optimistic outlook in the energy market. Oil exchange traded fund traders, on the other hand, have been quietly pulling out.

Over the past month, the United States Oil Fund (NYSEArca: USO), which tracks West Texas Intermediate crude oil futures, rose 16.0% and United States Brent Oil Fund (NYSEArca: BNO) gained 15.0%. [Traders Quick to Reap Profits in Oil ETFs]

WTI crude oil futures are now hovering around $58.8 per barrel and Brent crude oil futures were trading around $66.3 per barrel after a decline in U.S. rig counts and geopolitical tensions in the Middle East helped diminish the supply outlook.

However, Eugen Weinberg, head of Commodity Research at Commerzbank, warned that a rally in oil prices was “premature,” reports Holly Ellyatt for CNBC.

“I wouldn’t be surprised if we saw the current $59 go even below $50, should this rally stall and should we come to this correction,” Weinberg said on CNBC. “I think it’s more hopes driving the market rather than the real facts. I wouldn’t be surprised to see a short-term correction, a strong correction because of all the fundamental data. I think the rally is premature and would be probably looking for the prices (to go more) below $60 in a month’s time than above $70, for Brent.”

Oil ETF investors have already been growing more cautious as the price of oil spiked. For instance, investors yanked $587.2 million out of USO in April, according to ETF.com.