Rub the tenderloins (you'll probably have two for that amount of meat) all over with the olive oil and season with the salt and pepper. For each whole tenderloin, cut four 12-inch lengths of kitchen twine. Lay four of the strings horizontally on a work surface about 2 inches apart. Lay several sprigs of rosemary vertically on the strings. Set a tenderloin on top of the sprigs. Wrap the twine around the pork the pork and rosemary and tie so the rosemary is securely attached to the tenderloin; cut off any excess twine. Drizzle with a little more oil. Repeat for the other tenderloin.

Heat a gas grill to high or prepare a charcoal grill. Set the pork on the hot grill about 6 inches away from the heat. Cook uncovered, turning once, until the meat feels springy, not mushy, when squeezed (150 degrees to 155 degrees F) and the rosemary has darkened, 20 to 30 minutes. Take the pork off the grill; discard the rosemary and twine. Let the pork rest for a few minutes before you slice and serve.