Do not answer the poll if you do not use an automated trading system or if you feel, for any reason, that you cannot answer correctly. ---------------------------- The major categories of transaction costs are the following: 1. commission 2. bid-ask spread 3. slippage (delay in the execution usually gives you a worse execution price) 4. market impact (how your order will affect your own execution price) Whereas all 4 types of transaction costs in the future will be of concern to me, right now all I have to worry about, given my capital and my systems, is 1 and 2, (commission and spread). Besides, given the low frequency and average gain of my trades I almost don't have to worry about any costs at all. Any comments on the categories and how these costs affect your own automated trading? For example, I use MARKET orders. That's how little I am worried about 2, 3 and 4 (spread, slippage and market impact).