Oligomerization of isobutene has been investigated using several cation exchange resins in order to produce triisobutene that is useful feedstock for heavy alkylates and neo-acids. Trimer selectivity increases with increasing isobutene conversion. High isobutene conversion is obtained at high temperature and low space velocity by using macroporous cation exchange resins that have high concentration of sulfonic acid groups. Under selected conditions (viz., isobutene WHSV: 10 h -1; temperature: 70 oC; catalyst: Amberlyst-35), the isobutene is quantitatively oligomerized with more than or equal to 70 % selectivity for trimer. The wet resin catalysts containing water or ethanol show very high stability for the oligomerization up to about 70 h contrary to the gradual decrease of the conversion with dehydrated catalysts.