Oublier belong to the 1st
group. Oublier is a very common french verb.
Oublier is conjugated the same way that verbs that end in : -ier
Oublier is conjugated with auxiliary avoir
Oublier verb is
direct transitive, intransitive.
French verb oublier can be conjugated in the reflexive form: S'oublier
verb is a direct transitive verb, so passive voice can be used.