Preheat oven to 350 degrees F.
Mix jerk seasoning with the oil in a small bowl (this will thin it and cut the heat). Trim any excess fat from the pork loin, leaving a thin-layered wide strip down the center of the top. Evenly rub the entire pork loin with the jerk seasoning mixture. Place pork loin in a shallow greased roasting pan, and bake for 20 minutes. Then reduce the temperature to 300 degrees F and continue baking for about 1 more hour, or until a meat thermometer stuck in the thickest part reads 145 degrees F. Remove from oven and let rest for at least 10 minutes before slicing.