I'm trying to decide which ECN I should place my limit orders on. I am thinking the ECN with the highest internal volume which will give me the highest probability of getting filled in situations when the NBBO touches my limit price but does not travel through it. Iv been trying to figure out the internal volume at each. At this moment it says BATS: 25,061,071 Total Volume ARCA: 105,948,214 Volume NSDQ: 46,079,260 NLS Volume Unfortunately I cant tell if ARCA's volume is including all trades on SPY, or just internal matches. Does anyone know a singular resource which would tell me this information of internal volume? I also know another factor in deciding which ECN to target is the rebate structure, does anyone know a singular resource online which lists all current rebate information for various exchanges? Thanks.