Average Price

The average price of a stock purchase or sale is equal to the stock price of each lot multiplied by the share amount, divided by the total share bought or sold.

It is not uncommon for an order to be segmented and filled at different prices for each lot.  This tends to occur more frequently in thinly traded stocks or stocks that are moving quickly.  This “slippage” can sometimes be quite dramatic and is not a negligible cost of trading.