Abstract—Opportunistic routing (OR) has received much attention as a new routing paradigm due to its efficient utilization of broadcasting and spacial diversity of the wireless medium. Although numerous OR algorithms and protocols have been proposed to apply to various environments and integrate with numerous techniques, as far as we know, none of the existing works have used mathematical tools such as routing algebra to analyze the compatibility of routing metrics and routing protocols so as to provide a guideline for routing protocol design. In this paper, we design a new OR algebra based on the routing algebra proposed for inter-domain routing [1], identify the essential properties of OR in the mathematical language of the OR algebra, and analyze the design space in terms of routing metrics for various routing requirements.