"S&P 500 Options Quirk Sparks Manipulation Speculation, Rakes in Billions"

Unusual trading activity in the S&P 500 outside regular market hours is influencing the fate of stock options with a face value of trillions of dollars, according to new research. A monthly pattern sees key prices jump just before the expiration of derivatives tied to the benchmark US gauge, generating profits of roughly $3.8 billion per year for bullishly positioned investors. The authors of the study speculate that "manipulators" could be at work, taking advantage of a window of thin trading to push up the index and benefit their option positions. However, it is debatable whether this constitutes manipulation or is simply a pricing anomaly.