Texas regulators rejected NextEra Energy Inc.’s $18 billion bid to buy the state’s largest transmission operator, Oncor Electric Delivery Co., for a second time.

The Public Utility Commission of Texas first blocked the deal in April. On Wednesday, commissioners adopted an order that denied NextEra’s request for a rehearing on the merger.

Selling Oncor is key to ending the high-profile bankruptcy of parent Energy Future Holdings Corp. Formed by KKR & Co., TPG Capital and Goldman Sachs Capital Partners as part of the biggest leveraged buyout in history, Energy Future has been working to restructure almost $50 billion in debt since it filed for Chapter 11 in 2014.

“It’s back to the drawing board,” Paul Patterson, a utility analyst at Glenrock Associates LLC in New York, said in a phone interview. “The creditors have to think about what realistically will get through the Texas PUC.”

Robert Gould, chief communications officer at NextEra, declined to comment. Geoff Bailey, a spokesman for Oncor, had no comment.

An Oncor takeover proposed by a group backed by Hunt Consolidated Inc. similarly failed last year.

Commissioners expressed concerns throughout NextEra’s proceedings about the loss of ring-fencing measures designed to protect Oncor’s credit rating and who would ultimately control the board of the company.

The “fatal flaw” in NextEra’s application was its refusal to accept those measures, commissioner Brandy Marty Marquez said in a memo referring to the draft order. “Any benefits offered could not overcome that failure.”

Commissioner Kenneth Anderson filed a memo in which he said NextEra had “failed to meet its burden of proof” to show a transaction would be in the public’s interest. 

NextEra, owner of Florida’s largest utility, agreed to purchase Energy Future’s 80 percent stake in Oncor last year in a transaction that has been valued at more than $18 billion, including debt. A bankruptcy judge approved the sale in February.

NextEra rose 0.4 percent to $142.50 as of 12:23 p.m. in New York. The shares are up 19 percent so far this year.