Supercritical alkylation and butene dimerization were investigated using sulfated zirconia (SZ) and iron-manganese promoted sulfated zirconia catalysts (SFMZ), as a function of iso-butane/olefin (I/O) ratio and at temperatures between 60 and 155 degreesC. Detailed product analysis demonstrated that while C-8 yields were as high as 80 wt.%, neither catalyst produced significant quantities of trimethyl pentanes, although both had high selectivities to dimethyl hexenes. A comparison of 1-butene versus 2-butene as the olefin feed charge showed that 1-butene first isomerizes to 2-butene, which then produces C-8 products. In all cases, the products consisted primarily of C-8 olefins, which in turn was dominated by dimethyl hexenes. The addition of water at a concentration as low as 1.4 mol% was found to increase dimethyl hexene selectivity (94 wt.%), and lowered the deactivation rate by 30%. The dimerization of a straight 2-butene charge produced a C5+ yield in excess of 90 wt.%, with a 73 wt.% selectivity to dimethyl hexenes. Subsequent regenerations of this catalyst resulted in about 10% conversion loss/generation, but with minimal change in dimethyl hexene selectivities.