I've always been curious...does anyone know how much brokers have to pay when a trade is executed through them? Do they pay per share/per trade/both? And how much are ECN charges, really? All I know of for sure is that Real Tick (Townsend?) gets $3 per trade for each trade that is executed through that software. I've just always wondered how some firms can charge a penny a share and less, IB seems to eat all ECN fees, and yet most firms charge $15 and higher plus ECN fees. I don't know whether this will help anyone to know this, but this has always bugged me.