A process for making glycerol di-tert-butyl ethers is disclosed. In one aspect of the invention, glycerol and isobutylene react in the presence of a β-zeolite having a silicon to aluminum ratio greater than 150. In another aspect, the etherification is performed in the presence of a β-zeolite and added tert-butyl alcohol. Each process selectively provides glycerol di-tert-butyl ethers while reducing the generation of isobutylene dimers and trimers. Utilizing both aspects of the inventive process simultaneously affords a diether product mixture containing less than 5 wt. % of isobutylene oligomers.