On IB, I have a choice in the optiontrader platform that allows me to pick SPY as the underlying. It then gives me 8 exchanges to choose from. I'm assuming that I need to highlight 'smart', but 'AMEX' works as well. There are only small differences in the bid and ask, but there are differences. The price chart says spy@smart bid/ask and doesn't allow the word AMEX on the chart. The box I fill out just before the chart comes up has SPY as the underlying Exchange is SMART and Description is STOCK (AMEX) There is also a choice between MEXI and AMEX Please help. Joshua