The present disclosure relates to methods and systems for controlled delivery of unknown fluids that safely and efficiently removes entrained gas from unknown fluids in the wellbore and/or marine riser. A control system automatically controls one or more choke manifold(s), and optionally the flow rate of one or more mud pump(s), to maximize the safe flow rate of returning unknown fluids to one or more instrumented mud-gas separator(s) without overloading. The control system may receive the state of the one or more instrumented mud-gas separator(s) to manipulate the choke manifold(s), and optionally the one or more mud pump(s) to maximize the safe flow rate of return fluids and expedite the removal of gases.