The specific rates of solvolysis in 80% ethanol and 97% 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) for various tertiary alkyl chlorides having different steric requirement and experimental (FT ICR) gas-phase stabilities of the corresponding carbocations were determined. The experimental gas-phase stabilities were in good agreement with theoretical values computed at the MP2/6-311C(d,p) or the MP2/6-311G(d,p)//MP2/6-31G(d)(d) level. The relation of differential activation Gibbs energy changes for solvolysis [delta Delta G double dagger = -RT In(k/k(o))] (relative to 1-chloroadamantane) vs the experimental gas-phase cation-stabilities Delta G(o) (relative to l-adamantyl cation) was compared with the previously established similar relation for bridgehead systems. It was revealed that the solvolysis of tert-butyl chloride in 80% ethanol is nucleophilically assisted by 4-8 kcal mol(-1). The delta Delta G double dagger vs Delta G(o) relation for heavily crowded 4-chloro-2,2,3,6,6-pentamethylheptane was found to be comparable to that of bridgehead compounds. The reversal of the ranking of stabilities of the tert-butyl cation and 1-adamantyl cation on going from the gas phase to aqueous solution was computationally assessed. The results agree with the fact that larger substituents around a cationic center increase the stability of the ion in the gas phase thanks to their larger polarizability, and that this effect is either offset or even dramatically reversed in solution.