Marquee oil ETFs could see increased volatility ahead as lack of new investment catches up with oil industry.

Traders will especially be looking to the United States Oil Fund (NYSEArca: USO), which tracks West Texas Intermediate crude oil futures, and the United States Brent Oil Fund (NYSEArca: BNO), which tracks Brent crude oil futures.

Declining prices in recent years have prompted scores of major oil producers to rein in capital spending. Technological improvements and greater efficiency has helped U.S. shale producers pump out crude oil at lower margins – some say it is now profitable at less than $50 per barrel. Additionally, companies are finding easy access to credit and private-equity firms have bought out struggling companies, which have kept production flowing.

“Oil markets could experience more intense price volatility in the coming years because of insufficient investment in new production, according to the head of the International Energy Agency’s oil market and industry unit, Neil Atkinson,” reports OilPrice.com.

While U.S. shale producers previously continued pumping in the face of low prices, the industry has recently revealed a spate of capital spending reductions, indicating still low crude prices are taking a toll. Low oil prices are also prompting speculation about credit downgrades for some exploration and production firms that already carry junk credit ratings.

Related: Oil ETFs Lift on New Supply Data Report

Current OPEC compliance with production cut plans remains above their historical average, and it usually takes between two to three quarters for inventories to normalize after the cuts. While demand has yet to catch up to elevated supplies, rebounding economies in Europe and steady economic growth in the U.S. could at least keep oil prices steady around current levels in the second half of 2017.

“The problem with new investments, however, remains. Bahrain’s oil minister, speaking at the same event as the IEA official, said that although prices have improved lately, they are not high enough to motivate sufficient investment in new production,” according to OilPrice.com. “Bahrain’s top oil man is not the only one warning about a possible supply crunch, but given these officials’ vested interest in the effect of supply crunches on prices, their comments are better taken with a pinch of salt.”

Between 2014 and 2016, global oil companies reduced spending by a whopping 40%, efforts that included significant layoffs and withdrawals from projects seen as too expensive or unlikely to bear near-term profits.

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