1. Combine olive oil, butter, Dijon mustard, vinegar, garlic and black pepper in a small saucepan.
2. Whisk over low heat until the basting sauce mixture is melted and smooth.
3. Place swordfish steaks on a broiler pan or grill.
4. Brush the tops of the steaks with the basting sauce.
5. Broil or grill approximately 6 minutes. Turn, baste the other side, and broil or grill another 5 minutes.