A process for producing alkyl ethers, by etherification of tertiary C.sub.4-7 olefins with an alkanol, comprising carrying out the etherification in reactor train system primarily configured for dimerization of isoolefins. In the etherification, the ratio of alkanol-to-olefin is 0.5 to 2, calculated from the amount of tertiary C.sub.4-7 olefins of the fresh feedstock. The invention makes it possible to change the product of the process from dimer to ether and vice versa merely by adjusting specific flows within the process. The present kind of process is therefore readily adaptable to fluctuating market demands for various gasoline octane-boosters (isooctane or MTBE).