Negative streamer growth is observed in a highly refined mineral oil for sphere‐sphere electrode configurations. The shape of the streamers is somewhat different from that found in point‐plane geometries. The addition of electron trapping additives accelerates the negative streamer velocity as was found to be the case in point‐plane geometry. Breakdown occurs before the negative streamer crosses the gap and appears to originate at the anode. Very fast positive streamers are, in fact, observed.