Given the task definition and input, reply with output. This task is about writing a correct answer for the reading comprehension task. Based on the information provided in a given passage, you should identify the shortest continuous text span from the passage that serves as an answer to the given question. Avoid answers that are incorrect or provides incomplete justification for the question.

Passage: Prominent theatre companies in Oklahoma include, in the capital city, Oklahoma City Theatre Company, Carpenter Square Theatre, Oklahoma Shakespeare in the Park, and CityRep. CityRep is a professional company affording equity points to those performers and technical theatre professionals. In Tulsa, Oklahoma's oldest resident professional company is American Theatre Company, and Theatre Tulsa is the oldest community theatre company west of the Mississippi. Other companies in Tulsa include Heller Theatre and Tulsa Spotlight Theater. The cities of Norman, Lawton, and Stillwater, among others, also host well-reviewed community theatre companies. Question: What is the oldest resident professional theater company in Oklahoma?
American Theatre Company