the reason some gaps filland others don't is the cause of the gap. When unexpected news rather it is positive or negative occurs this causes a sudden excess of buyers or sellers. SInce it was on unexpected news those gaps will not fill. A run away gap usually occurs after there has been an event which caused a surge in vol and pirce. Many invedstors did not jump on that trade and were waitng for correction. When none occurs and they all jump at once they cause a gap which will fill latter. Short term traders often look for chart patters with gaps to play the long or short side of the game.Notice they gap we are discussing came on a surge of vol. many time greater than the averaage not just a above average.
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