Iv been doing a bit of research into figuring out if one order type has a bit of added value over the other. The tests are being done on a liquid equity (SPY) which normally has a 0.01$ spread. Both orders guaranteed a fill, trading 100 SPY at market is 0.50$ more expensive in ECN fees than trading a Pegged order (assuming adding liquidity). I don't have enough data yet to come to a conclusion, but was wondering if anyone on ET has experience researching or thoughts on this topic. Thanks Iv also noticed that some of my Pegged orders are removing liquidity, which is slightly confusing since it should peg to correct side of the spread.