(Bloomberg) -- An energy crunch has money mangers going all-in on energy ETFs to such a degree that they may be limiting the potential for fresh gains. 

While the outlook for exchange-traded funds tracking the sector remains positive, Citigroup Inc. strategists led by Scott Chronert warn the “astounding” level of bullishness hasn’t been this high in years -- shifting the risk-reward calculus.

Investors have poured roughly $19.9 billion into U.S. energy-focused equity funds so far this year in a bet global energy shortages will continue to jolt natural gas and electricity markets. Gains in commodity prices have helped lift shares of energy companies after several years of losses. Energy funds have seen a 48% year-to-date return on average, propelling the sector to be the best performing group in the S&P 500 index. But crowded positioning may limit upside leverage. 

“Net long positioning ultimately puts added pressure on positive commodity outlooks and Street revisions to follow-through into year-end, and likely moderates energy equity ETF upside leverage to oil prices,” Citi strategists said in a note to clients. “Still, while being long energy may look increasingly consensus, absolute returns can still push higher as inflation concerns, and oil prices press onward.” 

Citi strategists remain bullish on the energy space and recently raised their year-end price target for oil, with their bull case forecasting $90 a barrel for Brent crude oil. 

The firm isn’t the only one doubling down on energy either. Nadia Lovell, senior U.S. equity strategist at UBS, said in a Thursday interview on Bloomberg TV’s Surveillance that she continues to like energy despite its strong year-to-date performance. 

“When you look at energy it has the highest free cash flow yield, the highest dividend yield, the most earnings momentum right now, and we just don’t think the sector is pricing in where oil is right now,” Lovell said. 

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