Combine all the ingredients for the herb marinade in a large bowl or glass measuring cup. Stir well and reserve.
Place the pork tenderloins in a non-reactive baking dish that's just big enough to accommodate them and then pour about 2/3 of the marinade over them. Toss delicately until both tenderloins are completely coated and the herbs are well distributed, then cover with plastic wrap and place in the refrigerator to marinate for at least 24 hours, or up to 48 hours. Reserve remaining marinade to serve with the grilled meat.
When ready to eat, preheat your outdoor grill to medium-high heat, about 400°F, and take the reserved marinade out of the refrigerator so the olive oil has a chance to get back to its liquid state while the pork is grilling.
Remove the tenderloins from their marinade and brush off excess herbs; discard used marinade.
Grill the tenderloins for 15 to 20 minutes, until a meat thermometer registers 145°F. Turn 3 to 4 times during grilling to ensure even cooking.
Transfer the cooked tenderloins to a plate, spoon some of the reserved marinade over them and tent loosely with aluminum foil. Allow to rest for 10 minutes then slice into thick medallions and serve with the more of the reserved herb marinade.