The company will retain the SK Innovation name and combines its petrochemical and battery operations with SK E&S's liquefied natural gas and renewable energy businesses.
As part of a groupwide restructuring, the merger is seen as a strategy to turn around SK Innovation's struggling battery unit, SK On, by leveraging the strong cash flow of SK E&S.
SK On also completed its merger with SK Trading International on Friday.
"The merger has equipped us with a balanced energy portfolio, enabling us to draw a bigger picture for future growth," SK Innovation CEO Park Sang-kyu said in an email to employees.
SK E&S will continue operations as a company-in-company under the new name SK Innovation E&S, maintaining its existing organizational structure except for some integrated functions such as the board secretariat.
The newly merged company is exploring several synergy projects, including plans to establish self-generating power facilities using LNG at SK's Ulsan industrial complex and expanding renewable energy direct power purchase agreements.