Abu Dhabi's ADNOC has struck a deal to buy German chemicals maker Covestro for 14.7 billion euros ($16.3 billion), including debt, in the energy giant's biggest ever acquisition.

The tie-up is part of the oil producer’s big bet on chemicals, as it tries to transform into a fully integrated energy company.

Covestro AG, the Bayer spinout and plastics manufacturer whose North American headquarters is in Pittsburgh, is poised to be acquired by Adnoc International for about $18 billion.