In a shallow non-porous dish or bowl add olive oil to melted butter or margarine. Then add lemon juice, mustard, basil, garlic and salt and pepper to taste. Mix well and add shrimp to coat. Cover and refrigerate for 1 hour.
Preheat grill to high heat. Lightly oil grill grate. Remove shrimp from marinade and thread on skewers.
Place skewers on heated grill and cook about 2 minutes on each side.