Wash clams to remove any dirt or sand.In a large pot, heat oil over medium heat. Add garlic; saute for 1 minute, or until tender. Pour in the white wine. Boil until wine has reduced to half its original volume.Add clams, cover, and steam till clams start to open. Add butter, cover, and cook till most or all of the clams open. Discard any that do not open. Transfer clams and juice to 2 large bowls.