To achieve the degree of doneness you want, place a meat thermometer deep in the large end of the tenderloin and cook to 5 to 10 degrees below the desired temperature, or use an instant-read thermometer. The temperature for medium rare is 145F (63C), for medium 160F (71C), and for well done 170F (77C). When done, remove the roast and let it stand 15 to 20 minutes before carving. The roast will continue cooking as it stands.
Place the meat on a rack in a shallow roasting pan in a hot oven--425F (22C)--and cook until the meat reaches the desired degree of doneness, 50 to 70 minutes.
Brush the tenderloin with oil and place it directly over medium-high heat. Cook, turning occasionally, until the tenderloin roast reaches the desired degree of doneness, 35 to 60 minutes.
Heat oil in a deep skillet and brown the meat on all sides. Add cooking liquid and seasonings if desired, bring to a simmer, and then reduce the heat. Simmer 10 minutes per pound (445g) or until the tenderloin roast reaches the desired degree of doneness.