Order imbalance is a situation resulting from an excess of buy or sell orders for a specific security on a trading exchange, making it impossible to match the orders of buyers and sellers. For securities that are overseen by a market maker or specialist, shares may be brought in from a specified reserve to add liquidity, temporarily clearing out excess orders from the inventory so that the trading in the security can resume at an orderly level. Extreme cases of order imbalance may cause suspension of trading until the imbalance is resolved.