Improved hydrocarbon separation processes by the selective sorption properties of a novel class of zeolites are provided. The novel class of zeolites is characterized by a silica to alumina mole ratio greater than 12 and a constraint index within the approximate range of greater than about 2 to about 12. The separations encompassed by this invention include paraffins from aromatics, olefins from aromatics, olefins from paraffins, linear paraffins from branched paraffins, linear olefins from branched olefins, methyl branched hydrocarbons from more highly branched hydrocarbons, higher molecular weight components from lower molecular weight components within an homologous series, n-paraffins or methylparaffins from cycloparaffins, n-alkyl or methyl alkyl substituted aromatics from more highly branched isomers, mixed paraffins from aromatics (dewaxing), and non-aromatic methyl-branched hydrocarbons from aromatics. Also mono-substituted or para-disubstituted aromatics can be separated from ortho- and/or meta-disubstituted or more highly substituted aromatics. By reducing the diffusional rate characteristics of the aforesaid zeolites, improved separation of p-xylene from its isomers is also attained.