A ride-sharing server may receive, from a user, a vehicle-rental request including trip characteristics specifying an origin location, a destination location, and time constraints; identify another user having rental criteria matching that of the vehicle-rental request; send a rent-share request to the user and the other user to rent-share as a joint-rental group; and rent a vehicle to the joint-rental group when the rent-share request is confirmed. A mobile device of a ride-sharing user may send, to a rent-sharing server, a vehicle-rental request including trip characteristics specifying an origin location, a destination location, and time constraints; receive, from the rent-sharing server, a rent-share request to rent-share a vehicle as a joint-rental group including another user having rental criteria matching that of the vehicle-rental request; and responsive to the rent-share request, rent the vehicle as the joint-rental group.