Woodside Energy will spend $US2.35 billion ($3.7 billion) to purchase a gas-based ammonia project on the US Gulf Coast, representing its biggest investment yet in lower-carbon energy but fuelling market concerns that shareholder returns will suffer.

The cash acquisition of OCI Clean Ammonia Holding and its ammonia project under construction in Texas comes just two weeks after Woodside struck a $US900 million deal to buy the Driftwood LNG export venture in Louisiana, which will significantly increase its LNG production and trading capacity.