I think if you get there early, you'll get in, no problem. We got there at opening on a Sunday and were among the first seated, and we had a party of 8. I had called before leaving home to see if we could get a reservation; I called T-Rex directly and nothing was available on our arrival night except really early and really late. The girl I spoke with said they only take reservations for something like 20% of their tables and the rest are for walk-ups. This was back in May, so it may have changed, but there were lines of people waiting for tables, so I don't think they turn anyone away.