Abu Dhabi National Oil Company (ADNOC) is finalising due diligence for a takeover of Covestro in a deal that could reach 11.7 billion euros ($13 billion), two sources familiar with the matter told Reuters on Wednesday.

An announcement could come in September as the process enters its final phase, with a price of 62 euros per Covestro share still on the table, the sources said.

Covestro and ADNOC declined to comment. Bloomberg first reported the news on Wednesday.

Covestro shares rose as much as 5.7% to 56.90 euros, reaching their highest level in almost three years.

The Leverkusen-based plastics company announced at the end of June that it would enter into concrete negotiations with ADNOC. After months of canvassing, the oil company announced a possible offer of 62 euros per share, subject to due diligence.

Covestro finance chief Christian Baier told Reuters at the end of July that there had been progress in the talks and that the negotiations were continuing to be very constructive.

Covestro is the former plastics subsidiary of Bayer , which the pharmaceutical and agricultural group took public in 2015.

The company employs around 17,500 people worldwide, with almost 7,000 in Germany. Covestro manufactures intermediate products for the automotive, furniture, household appliance and construction industries. Its products can be found in mattress foam and car seats, as well as in wind turbine blades.

($1 = 0.9001 euros)

(Reporting by Emma-Victoria Farr in Frankfurt, additional reporting by Patricia Weiss and Yousef Saba, editing by Jason Neely and Mark Potter)