In a shallow baking dish, mix soy sauce, sherry, vegetable oil, fresh lime juice and garlic. Add the tuna steaks, and turn to coat. Cover, and refrigerate for at least 1 hour.
2.
Preheat barbecue to medium high heat. Lightly oil the cooking grate.
3.
Place tuna steaks on the preheated barbecue, and discard remaining marinade. Grill for 3 to 6 minutes per side, or to desired doneness.