Heat oil in a skillet over medium heat. Add roast and brown on all sides; remove to a large slow cooker and set aside. Mix soup, catsup, vinegar and brown sugar; pour over roast.
Cover and cook on low setting for 8 to 10 hours, until roast is fork-tender. Remove roast to a platter; discard string and let stand for 10 minutes.
Shred roast, using 2 forks; return to slow cooker and stir. Spoon meat and sauce onto bread slices or rolls.