This invention relates to a process, comprising reacting ethylene and oxygen or a source of oxygen in the presence of a catalyst in a reactor to form a product comprising ethylene oxide, wherein the catalyst contains silver or silver compound and a support and the catalyst is in the form of particulate solids having a mean particle diameter from 1 to 1000 [mu]m and wherein the molar ratio of oxygen to ethylene is from 1:4 to 10:1.