The invention pertains to a catalyst useful for the epoxidation of an olefin. More particularly, the invention pertains to an improved catalyst useful for the epoxidation of ethylene to ethylene oxide. The catalyst has improved selectivity in the epoxidation process. The catalyst comprises a solid support having a surface, which has a first mode of pores which have a diameter ranging from about 0.01 μm to about 5 μm and having a differential pore volume peak in the range of from about 0.01 μm to about 5 μm. The surface then has a second mode of pores, different from the first mode of pores, which second mode of pores have a diameter ranging from about 1 μm to about 20 μm and have a differential pore volume peak in the range of from about 1 μm to about 20 μm. On the bimodal pore surface is a catalytically effective amount of silver or a silver-containing compound, a promoting amount of rhenium or a rhenium-containing compound, and a promoting amount of one or more alkali metals or alkali-metal-containing compounds.