a process is disclosed for the highly selective skeletal isomerization of linear olefin - containing organic feeds wherein linear olefins , e . g ., n - butenes , are contacted with catalyst comprising zsm - 35 under isomerization conditions to produce iso - olefins of corresponding carbon number , e . g ., isobutene . high iso - olefin selectivities thus can be obtained , even at relatively low temperatures and high linear olefin partial pressures .