Hi. I am in process of putting my first automated trading system into production. It uses Interactive Brokers. Part of what it trades are commodity etfs and it does a form of trend following. It place orders a fixed times (10.45, 11.45, 12.45 ... 15.45, New York time) and it always does market orders. It will hold a position for around a week. I am wondering whether using market orders will be a problem given the liquidity of the instruments the system will trade. The least liquid of the funds is PowerShares DB Commodity Index (AMEX : DBC): http://finance.google.com/finance?q=dbc&hl=en Is the implied spread I get using Interactive Brokers' paper trading realistic? Or do I need to do some more refined order placement - i.e. a limit order.