Legendary hedge fund CEO and investment manager Kenneth Griffin doubled down on shale gas stocks in the third quarter, banking on higher share prices across the sector as investors anticipate a sharp increase in winter commodity gas prices.

Griffin's Citadel Advisors LLC more than doubled its stakes in pure-play shale gas exploration and production companies CNX Resources Corp., Antero Resources Corp., Comstock Resources Inc., and National Fuel Gas Co. in the third quarter, according to institutional investor filings with the SEC. All four saw their share prices rise since the third quarter began, led by Antero, which was up 66% through Nov. 23.

Griffin's touch was not universally aligned with the sector's improved performers. Citadel trimmed its stake in the largest U.S. gas producer, Appalachian driller EQT Corp., by 68% in the quarter while EQT shares have gained 30% in the second half of the year.

Other institutions shared Griffin's confidence in the sector, buying more shares in six companies than they sold in four others.

One standout stock buy was hedge fund Zimmer Partners LP's $60 million purchase of 4% of southwest Pennsylvania natural gas and NGL driller Southwestern Energy Co. While the new stake was just beneath the 5% threshold requiring a fund to declare its intentions, Zimmer has no history of activism, according to S&P Global Market Intelligence data. Southwestern's shares have climbed 22% since the third quarter began.

Big index funds such as Vanguard Group and Dimensional Fund Advisors LP cut their holdings sharply in Utica Shale driller Gulfport Energy Corp. before Gulfport's Nov. 13 filing for bankruptcy protection, but Charles Schwab Investment Management Inc. and tiny investment adviser Shah Capital Management Inc. were not so quick. Both funds added to their position in the quarter before Gulfport filed.