Alcohols add to electrophilically activated alkenes.  The method is atom-economical:
: RC=CR + R–OH → RCH–C(–O–R)–R
Acid catalysis is required for this reaction. Commericially important ethers prepared in this way are derived from isobutene or isoamylene, which protonate to give relatively stable carbocations.  Using ethanol and methanol with these two alkenes, four fuel-grade ethers are produced:  methyl tert-butyl ether (MTBE), methyl tert-amyl ether (TAME), ethyl tert-butyl ether (ETBE), and ethyl tert-amyl ether (TAEE).
Solid acid catalysts are typically used to promote this reaction.