Orange Country-Style Ribs

2 pounds pork country-style ribs, all visible fat removed
1 tablespoon olive oil
1 (6 ounce) can tomato paste
1/2 cup packed brown sugar
1/4 cup frozen orange juice concentrate, thawed
2 tablespoons red wine vinegar
1 tablespoon prepared mustard
1 tablespoon Worcestershire sauce
1/2 teaspoon pepper

Cut ribs if necessary to fit crock pot.

Combine sauce ingredients; mix well. Pour over ribs. Cover; cook on LOW for 5 hours, adding orange juice if necessary after 3 1/2 hours.