Disclosed are methods for finding all valid paths in a COBOL program. These methods are performed in polynomial time, allowing them to be scaled to accommodate large COBOL programs. As the methods find all valid paths in COBOL program code, by traversing and marking the nodes of the program upon being traversed. Accordingly, all usable and reachable code is indicated and marked. This increases safety when working with the code, as removal or alteration of such valid code is indicated, and thus, made unlikely.