Dow Chemical Co. and the Saudi Arabian Oil Co. have signed a deal to build a $20 billion chemical complex in the kingdom.

The two companies’ boards said in a statement Saturday that their joint venture, dubbed the Sadara Chemical Co., formalizes a project that has been in the works since 2007. It promises to create the largest integrated chemical facility ever built in one go.

Production could start as early as the second half of 2015.

The complex will be located in Jubail Industrial City, about 60 miles (100 kilometers) northwest of the eastern Saudi city of Dammam. It will include 26 manufacturing units producing chemical products and plastics for use in the energy, transportation and infrastructure industries.