Remove loose paper skins from garlic heads but leave them whole and unpeeled. Cut enough off the top of each head to expose all the cloves.
If roasting three or fewer heads place them on a square of foil root side down, drizzle with oil and wrap tightly. If roasting several heads place prepared heads in an oiled pie pan, root side down and drizzle heads with olive oil. Cover pan tightly with aluminum foil.
Bake 30 to 60 minutes. Heads are roasted when the garlic inside the cloves is very soft and the head looks golden or lightly brown. If not done when checked, rewrap tightly and return to the oven until garlic reaches desired doneness.
To use, gently squeeze the head until individual cloves pop out