Renewable hydrogen produced via water electrolysis has a pivotal role in decarbonizing the hard to abate sectors. As water

electrolyzer plants scale up, their operations influence the power system stability and electricity markets. Frameworks for elec-

trolyzer participation in electricity balancing markets are under active development. Nonetheless, their potential participation

depends on both their technical capability and the associated economic benefit under prevailing market rules. This work evalu-

ates the economics of electrolysers providing frequency containment reserve (FCR), while taking into consideration limitations

of the electrolyser technology and electricity market constraints. It uses 2025 historical price and frequency data for Denmark,

Germany and the Netherlands. A mixed integer linear program is used to co-optimize the electricity procurement in day ahead

market and FCR provision. Results show that participation in FCR enhances the economic performance of and the capacity factor

of the electrolyser plant. Moreover, the sensitivity to FCR procurement design is evaluated, demonstrating that a potential 1-hour

FCR block product could lead to even higher revenue increase, compared to the 4-hour block of today.