Since 1982, the Monday of options expiration week has a bullish bias for S&P 500 and Russell 2000. S&P 500 has advanced 24 times in 34 years with an average gain of 0.81%. Russell 2000 has a nearly identical record, advancing 23 times in the same number of years, buts it average gain is slightly more than half that of the S&P 500 at 0.44%. Of note is the small-cap index streak of 17 straight advances from 1990 through 2006 and it has been down in four of the last six years. Expiration day (Friday) is far less bullish with average losses across the board. Expiration week as a whole usually does result in a modest weekly gain. The week after has been especially volatile with large swings in both directions punctuated by heavy losses in 1987 (Black Monday) and 2008 (Financial Crisis).