When drawn from a flame by an electric field, ion and electron collisions with neutral gas molecules influence flame shape, combustion intensity, soot formation, and the ion production rate. We describe these behaviors as they relate to the voltage-current relationship of a coflowing non-premixed methane/air flame. Simultaneous measurements of CH* chemiluminescence and ion current confirm a scaling relationship between these properties at saturation conditions. Separate mechanisms, depending on polarity, adequately explain additional current measured beyond saturation. Finally, flame oscillations observed at the transition to saturation ion current under certain flow conditions suggest a competition between two forces. The reason for this behavior is not clear; however, plausible mechanisms are identified. (C) 2015 The Combustion Institute. Published by Elsevier Inc. All rights reserved.