some primitive questions from a newer trader, for someone that understands or knows the inner workings of these exchanges. 1) What mechanism is in place to ensure minis move the same as the small contract? Is it purely up to buyers, sellers, and arbs? Or does the exchange do something to adjust price? 2) Same thing makes me curious about movement of different calendar months being the same between minis and the main contracts -- is this purely done by arbs? (i would think the risk might be too large arbing this since liquidity is often low and prices tend to move opposing directions quickly in certain contracts (ie nat gas)) 3) kind of related (and my intuition to answer #1 and #2): on market depth i often see buy/sell bids on qm and qg that hover simultaneously lower and higher than last traded prices of large number of contracts (ie 50 buy at 5.80, 50 sell at 5.90 - all will trade price may be 5.85). Is it safe to assume this is computer program arb? These bids seem to often float and move quickly - is this arb (or bid/ask manipulation) done by the exchange itself as a service to keep minis priced the same as big contracts, then? And lastly, is it actually arb or are these superficial orders created by a nymex program that don't get filled (i never buy blocks of 50 contracts) even if the opposing side hits the price ?? I just can't imagine the exchange arbing and risking such huge loss on illiquid contracts that can turn on a dime, but at the same time there has to be a mechanism in place to keep minis priced the same as big contracts. that's my common sense.