US chemical giants DuPont and Dow Chemical Co have agreed to merge in an all-stock deal valuing the combined company at $US130 billion ($A178 billion), with plans to eventually split into three.
The deal, which is likely to face intense regulatory scrutiny, allows the new company - to be called DowDuPont - to rejig assets based on their diverging fortunes.
The planned split would create companies focused on agriculture, materials and specialty products.
Dow and DuPont shareholders will each own about 50 per cent of DowDuPont.
DuPont Chief Executive Ed Breen will be CEO of the new company, while Dow Chemical CEO Andrew Liveris will be executive chairman.
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"This transaction is a game-changer for our industry and reflects the culmination of a vision we have had for more than a decade to bring together these two powerful innovation and material science leaders," Liveris said in a statement.
Dow Chemical shareholders will get one DowDuPont share for each Dow Chemical share they hold, while DuPont shareholders will get 1.282 shares in DowDuPont for each DuPont share they own.
DuPont shares were down about 4 per cent at $71.60 in pre-market trading on Friday, while Dow shares were up 1.6 per cent at $55.77.
