The following are some guidelines to help with trading the open.
GAP – Any day that the futures market opens up outside of the prior days Regular Trading Hours (RTH) trading range.
An opening price outside of this range put these guidelines in play.
1 – Bias is with the direction of an opening GAP that does not fill right way. What this means is if after the opening GAP up or down prices don’t begin to correct the opening trade imbalance, then the probability is that price will continue to move (up or down) in the direction of the GAP.
2 – Larger GAPs, as can be seen in the example below, will often go on unfilled or only fill partially and reverse back in the direction of the opening GAP.

3 – If the opening GAP fills, which means price returns to the closing price of the previous days Regular Trading Hours (RTH) Closing Price, and does not continue in that direction, the probability is that there will be and end of day (EOD) rally if the opening GAP was a Bullish GAP or a end of day sell off if the GAP was a Bearish GAP.
4 – GAPS of 10 SP/ES points or more are often difficult to trade. The market tends to trade sideways (choppy) while the opening trade imbalance is ‘digested’. It is best to avoid early trading and watch for the market to show its hand.