NextEra to buy Quantum-backed energy firm Caliber, set up US shale JV, sources say
By Shariq Khan NEW YORK, May 20 (Reuters) - NextEra Energy has agreed to buy U.S. oil and gas investment firm Caliber Resource Partners for $1.3 billion and has separately set up a joint venture with Caliber's private equity backer, Quantum Capital Group, to manage the power company's U.S. shale 
