Which 1987 trading technology helped accelerate selling during Black Monday?

Program trading helped accelerate selling during Black Monday in 1987.

Program trading used computer instructions to buy or sell baskets of stocks, often in response to movements in stock-index futures or predefined portfolio rules. During the 1987 crash, these strategies were associated especially with portfolio insurance, which sought to reduce losses by selling as markets declined.

As prices fell, automated or formula-driven selling added to the pressure. The interaction between futures markets and individual shares made the decline faster and more difficult to manage. The exact contribution of program trading remains debated, but it is widely recognized as one factor that intensified the crash.

The episode led regulators and exchanges to reconsider market structure. Circuit breakers, coordinated trading rules, and improved communication between futures and stock markets were introduced or strengthened. Program trading was not the sole cause; valuation concerns, interest rates, and investor psychology also mattered.