Transformation of linear butenes and iso-butene was carried out over H-FER (Si/Al ratio of 8) in a wide temperature and pressure range and with varying contact times. Catalyst lifetime over 100 h could be achieved by eliminating small traces of contamination, which accelerate deactivation, from the feed. The kinetic analysis revealed a close connection between iso-butene and octene formation and suggested a different pathway for propene and pentenes than for iso-butene. Low-pressure experiments showed very high initial selectivity to iso-butene at 40 mol% conversion, suggesting that coke does not play a significant role in the selective skeletal isomerization leading to iso-butene. Strong desorption limitations seem to exist, which are gradually reduced at higher temperatures. A new approach of the operational mechanism is introduced, where the regain of intrinsic selectivity of FER is proposed to occur by deactivation of the coke deposited in the pores.