Key establishment is a critical security issue for wireless sensor networks. Due to resource constraints on the sensors, public key based protocols are not suitable. In addition, conventional symmetric encryption based protocols require significant sensor memory. In this paper, we propose a new hybrid key establishment protocol based on a scheme by Blom and random key pre-distribution. In the proposed protocol, we use deployment knowledge and a new model to distribute key materials among sensors. The network area is divided into non-overlapping hexagonal cells, and key establishment between sensors in a cell is provided by the Blom scheme. Key establishment between sensors residing in neighboring cells is provided via pre-distributed random keys. The proposed protocol provides excellent performance with efficient resource consumption