Under the deal, Westmoreland will supply coal from its mine located in the southwest corner of Wyoming.
The latest deal will replace two existing contracts, set to terminate in 2016 and 2021, and the contracts will now extend until 2026.
Westmoreland Coal CEO Keith E Alessi said: "Westmoreland views FMC as a key partner at our Kemmerer Mine.
"The contract extension provides Westmoreland an additional long-term cornerstone industrial customer at our Kemmerer Mine and we anticipate a continuing positive partnership."
FMC Alkali Chemicals global business director vice president Tom Schneberger said: "FMC is pleased to optimize and extend our contract with Westmoreland Coal as it gives us long-term, stable access to an important energy source."
The company’s coal operations include sub-bituminous and lignite coal mining in the Western US and Canada.
