# Use Capacity Reservations to reserve On-Demand capacity in EC2 Fleet
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You can configure a fleet to use On-Demand Capacity Reservations first when launching On-Demand Instances by setting the usage strategy for Capacity Reservations to `use-capacity-reservations-first`. You can use this setting in conjunction with the allocation strategy for On-Demand Instances (`lowest-price` or `prioritized`).

When unused Capacity Reservations are used to fulfil On-Demand capacity:
+ The fleet uses unused Capacity Reservations to fulfill On-Demand capacity up to the target On-Demand capacity.
+ If multiple instance pools have unused Capacity Reservations, the On-Demand allocation strategy (`lowest-price` or `prioritized`) is applied.
+ If the number of unused Capacity Reservations is less than the On-Demand target capacity, the remaining On-Demand target capacity is launched according to the On-Demand allocation strategy (`lowest-price` or `prioritized`).

You can only use unused On-Demand Capacity Reservations for fleets of type `instant`.

For examples of how to configure a fleet to use Capacity Reservations to fulfil On-Demand capacity, see [Example CLI configurations for EC2 Fleet](ec2-fleet-examples.md). For more information, see [Reserve compute capacity with EC2 On-Demand Capacity Reservations](ec2-capacity-reservations.md) and the [On-Demand Capacity Reservation FAQs](https://www.amazonaws.cn/ec2/faqs/#On-Demand_Capacity_Reservation).