No all gaps do not fill. However, when we are as close as we are now the odds go up considerably. Had we not broken major support lines then the gap may not have closed. We have already hit .40 today so .37-.38 is now very close. Is it an absolute, no, but odds now are over 75%. Many people will set a limit order just above a gap if downward pressure is not too strong. Volume also plays a role.