Sources close to the negotiations indicate that Tesla Motors Inc and SolarCity Corp are making progress on an agreement that would merge the automaker and energy services company.

Both sides are reportedly conducting due diligence on each other, with the possibility of a deal between the two firms being completed in the next few days.

In June, Tesla announced that it had extended a $2.8 billion stock offer to acquire SolarCity, maintaining that the combined companies would allow consumers to single-source electric vehicles, solar panels and battery systems from one established brand.

Elon Musk, who serves as both Tesla CEO and chairman of SolarCity, is the largest single shareholder in both companies.

In a July 20 update of his “master plan”, Musk said that integrated energy storage and generation solutions would only be viable if Tesla and SolarCity were to “combine and break down the barriers inherent to being separate companies.”