The Exchange-Traded Markets are essentially only derivative markets and are similar to equity derivatives in their working. i.e. everything is standardized and a person can purchase a contract by paying only a percentage of the contract value. A person can also go short on these exchanges.
Also, even though there is a provision for delivery most of the contracts are squared-off before expiry and are settled in cash.
As a result, one can see an active participation by people who are not associated with the commodity.
Commodity Investment Strategies 
What is hedging and speculating 
Why Should You Invest in Commodities? 
What are commodity exchanges? 
How are Oil Prices determined? 
Who regulates the Commodity Market? 
What is a Futures contract? 
Technical Terms 
Physical and Futures Commodity Markets 
How to trade in Commodity Futures 
What is a Commodity Market? 
Evolution of Futures Market 
Benefits of Futures Trading