Endeavor Energy Resources , owned by the family of onetime billionaire and reality TV persona Autry Stephens, was the seller of properties in the Permian Basin's Midland Basin to the Blackstone Group (BX - Get Report) -backed Guidon Energy for $500 million, sources said Friday.

Blackstone, which announced the backing of Guidon late Thursday, wouldn't comment and Endeavor CFO Damon Button and general counsel Mike Short didn't respond to requests for comment.

The sale should help the Midland, Texas-based Endeavor pay down its debt load, which is estimated at around $1 billion. While the maturity on its revolving credit facility doesn't hit until 2019 and its senior bonds not until 2021 and 2023, rating agencies have raised concerns about compliance with covenants on the revolver, which could lead lenders to declare default in the case of a breach.

Moody's Investors Service said in a report Feb. 23 that unless the company sold assets, it would have to continue to rely heavily on its revolver to fund its $200 million capital spending program, further straining its liquidity. It noted that the company in January sold some of its Delaware Basin assets, including leases and production, for $123 million, which was used to repay part of its revolver outstandings.

That deal followed farm-out agreements executed with Exxon Mobil  (XOM - Get Report) unit XTO Energy in 2014 and 2015 that brought in cash and $459 million in asset sales through the first nine months of 2015. Moody's said Endeavor's 480,000 net acres continues to rank it among some of the largest exploration and production companies in the Permian Basin but its production and reserves are small compared with such Permian peers as Pioneer Natural Resources (PXD - Get Report) and Concho Resources (CXO - Get Report) . Almost 80% of its acreage is in the Midland Basin, Moody's said. Stephens appeared in the reality TV show Black Gold.  -- Lisa Allen contributed to this report