Clean mushrooms and place on paper towel to dry. Remove mushroom stems and mince stems finely.
Sauté mushroom stems and minced garlic in a frying pan in 2 tablespoons of the butter until lightly browned.
Drain crabmeat. Combine it with the cooked mushroom stems, bread crumbs, Parmesan cheese, sherry, oregano, salt and pepper and mix all well.
Slowly sauté mushroom caps in remaining 2 tablespoons of butter until tender, turning once. Remove and drain on a paper towel.
Stuff caps with crab mixture and place on a baking sheet. Place under broiler for 1-2 minutes until bubbly.