Type II compressed natural gas (CNG) storage vessels for automobiles are becoming widely used. They are not only supplied to automakers in Korea (such as Hyundai Motors), but are being exported overseas in increasing numbers. Autofrettage is a process that produces beneficial residual stresses in a vessel by subjecting it to excessive internal pressure. This strengthens the vessel and improves its fatigue resistance. This paper presents research into the autofrettage process and the residual stresses it produces in type II CNG storage vessels. Finite element analysis and a closed-form equation are used. Fatigue resistance is then analyzed via a fatigue evaluation performed according to ASME section VIII.