How does pre-market mechanism work and how is the opening price determined of a stock! How does pre-market mechanism work and how is the opening price determined of a stock! To protect small investors against this, a pre-market opening session was introduced to ensure orderly price discovery during the most volatile times Karan Dsij / Saturday, February 25, 2023 / Article rating: 4.1 Based on the principle of demand supply mechanism, exchange will arrive at the equilibrium price – the price at which the maximum number of shares can be bought / sold.