Apparatus, methods, and computer-readable media for on-demand sensing based on sidelink resource reevaluation are disclosed herein. An example method of wireless communication at a first user equipment (UE) includes selecting first sidelink resources for one or more transmissions based on partial sensing or resource selection independent of a sensing operation. The example method also includes receiving, over a sidelink channel, a resource reservation from a second UE, the resource reservation indicating reservation of resources overlapping with at least a portion of the first sidelink resources of the first UE. The example method also includes performing a resource reevaluation for one or more slots when the resource reservation indicates the reservation of resources overlapping with the at least a portion of the first sidelink resources of the first UE. The example method also includes selecting second sidelink resources for the one or more transmissions based on the resource reevaluation.