Preheat oven to 350 degrees F.
In a small bowl, combine thyme, garlic powder and onion powder.
Rub the pork loin roast with oil and season with salt and freshly cracked pepper. Season with thyme mixture, pressing into the meat, making sure to coat the entire surface with the seasoning.
Place the roast on a rack in a shallow roasting pan, and cook 90 minutes or until meat reaches an internal temperature of 160 F.
Remove from heat, cover with foil, and let sit 15 minutes before slicing. Serves 4 to 6.