Hi, I read a past thread saying that SPY and QQQQ are not shortable under Interactive Brokers. However, I have checked their shortable lists and both SPYs and QQQQs are there. I have also checked that USO is there but when I check the "availability", it is "3,000". How I am supposed to know that I can short, say, USO given the availability amount? Are all 3 of them shortable? Really appreciate if someone could clears things up.