Quote from NoDoji:
I have what may a stupid question, but I don't care because real traders no longer have egos and are quite content to ask stupid questions 
I notice often that there is small size at the bid and ask (as in my example here), and a large print hits the bid or ask and price doesn't move. The bid/ask stays the same. The way I interpret it, someone got filled at a price on far more contracts than the market depth was showing at that price.
Is that because of hidden orders that don't print until the entire order is filled, or...???
I've spent a lot of time watching CL time & sales (not dome bid/ask) flow to gauge what type of size is scaleable before slippage is a constant issue.
I consider shown bid/ask to be worthless information and only executed trades on time & sales to be of any value. You can see a lot of 100-lot orders trading without moving the market 1 cent, all day long.
Those orders on time & sales are often broken into pieces like:
24
12
4
7
3
1
1
4
4
5
3
2
etc... executed to the same 10th of a second. Those are clearly someone's entry or exit on 100-lot that is broken into the other side of opposing trades
True block orders for 50, 100 and more contracts often clear 1 cent above the ask or 1 cent below the bid. Those are likely off-exchange trades OR part of spreads where both legs of the spread fill at once. Perhaps the other side of those spreads in back-month contract likewise clear at -1 cent premium for execution but big spread traders factor in slippage as part of the natural process.
Bottom line is CL traders can clear 50-lot and 100-lot orders with acceptable slippage but that won't happen in tick-banger fashion all over the chart. There is a difference between flipping one-lots twenty times a day and working 50-lot orders inside one or two directional pushes per day.
In the end there is good money to be made trading 1-lots and vulgar profit potential trading big blocks. It's all good, any way you opt to slice it
