Abandoned underground coal mine areas must either be sealed or ventilated to comply with federal mine regulations. Ventilation of these abandoned areas is often impractical owing to roof falls and inadequate primary mine ventilation. If the area is sealed, a very complex ventilation system is set up, in which the gob "breathes" in and out owing to barometric pressure fluctuations. The gob assistant is a computer program (for use on IBM-compatible personal computers) which allows the prediction of air flows into and out of a sealed mine area. Gas flows with applicable control techniques are also modeled. This information is presented to the user, who will decide which control technique, or combination of techniques, will ultimately be applied. The gob assistant is an intelligent gob simulator that can reduce the guesswork involved in predicting the effects of sealing and control techniques before they are applied. This paper provides the fundamental principles upon which the gob assistant is based, verification of these principles, and an explanation of how these principles were integrated into the gob assistant.