what was not entirely clear:
will you yourself be the counterparty in this trade?
or are you also matching buyers+sellers but for options?
Thanks for the question.
Things are not set up for me to be a counterparty, but I could be. The system simply lets anyone create an option then sell it on the open market. Let me walk through an example. You are user-A and I am user-B.
user-A (you) decide to create a CALL 100 option for 1 year from now, with strike price of $5. You don't think much about the future of bitcoins. You think they will hold steady at $5.
You buy 100 bitcoins on Mt.Gox and use that to create your option on BitcoinOPX. You then place that option on sale with a price of $100, which you think is a good deal for having your money locked away for 1 year (20% return if you're right).
user-B sees this option, but I'm a big believer in Bitcoin. I think 1 year from now they will be at least $20 each, probably more like $50. That means I would have the right to buy 100 bitcoins at a cost of $500 at Maturity. However, my projection is their true value would be 100 x $20 (or $50) = $2,000 (or $5,000). That's a profit of $1,500 (or $4,500) if I'm right.
At that rate I think paying $100 for the option is a good deal.
When you create the option the bitcoins are placed in escrow with an independent escrow service. This means all options can be settled, if need be, without BitcoinOPX in the picture at all (say if shut down for legal reasons). However, with things running normally, every Friday when options mature BitcoinOPX requests back the required number of bitcoins from BTCrow, and settles all member accounts appropriately.
I hope that makes sense.
Edit: I changed the above wording to a more logical thought pattern for profit from each user's perspective.
This works with a call option but does not work with a put option.
user-A (you) decide to create a PUT 100 option for 1 year from now, with strike price of $5. You don't think much about the value of bitcoins dropping. You think they will hold steady at $5 or maybe rise.
You buy 100 bitcoins on Mt.Gox and use that to create your option on BitcoinOPX. You then place that option on sale with a price of $100, which you think is a good deal for having your money locked away for 1 year (20% return or more if you're right as your collateral bitcoins can also go up in value).
user-B sees this option, but I'm a big believer in Bitcoin crashing. I think 1 year from now they will be no more than $0.004 each, probably more like $0.001 each. That means I would have the right to sell 100 bitcoins at a cost of $500 at Maturity. However, my projection is their true value would be 100 x $0.004 (or $0.001) = $0.40 (or $0.10). That's a profit of $499.60 (or $499.90) if I'm right.
At that rate I think paying $100 for the option is a good deal. But there is a problem the collateral backing up my $499,60 or $499.90 profit is only worth $0.40 or $0.10 as the case me be. Ouch!
Moral: You need to escrow USD and BTC not just BTC.