In a small bowl, mix vegetable oil, soy sauce, vinegar, ketchup, and crushed garlic. Place flank steak in a large resealable plastic bag. Pour the marinade over steak. Seal, and marinate in the refrigerator at least 3 hours.
Preheat grill for high heat.
Oil the grill grate. Place steaks on the grill, and discard marinade. Cook for 5 minutes per side, or to desired doneness.
