per this handy graph, it seems more gravitates to 17.5 than 20. probably would be 17.5 + 20 / 2 = 18.75. totally unscientific method. lol. (because there are twice as much calls at 20 than puts at 20). <A HREF="http://www.schaeffersresearch.com/streetools/indicators/equity_oi_config.aspx" target="_new">http://www.schaeffersresearch.com/streetools/indicators/equity_oi_config.aspx</A>