Dacoinminster, your idea depends on bitcoin (almost) always going up. That's what I don't like about it. In case of default, you can't print more bitcoins outside the bitcoin network, just IOUs.

vector76, what if we have the derivative contracts inside the chain an also an automated broker that liquidates/covers your position if the reserves get too low?
This way, you eliminate the default risk. If you want your position to exist longer, just put more funds in the escrow.
To make them fungible, the "additional funds" (the difference between the needed funds and the actual funds), should be returned to the seller when the oil-coin is sold. The buyer of the oil-coin can add more funds to the contract within the same transaction to avoid the contract to be liquidated because of a small change in price a block after the transaction is made.

I think it could work, but yes, you would need a counter-party in the derivative for each oil-coin issued. All contracts would be btc (or derivativecoin) denominated.

The network would rely on derivativecoin creation and/or in fees for the contracts creation and trades. The fees can be charged in bitcoins, derivativecoins or both.
There's no need to create another currency for this though. This way we could also see if fees are enough on their own.