Hi there,
The opportunity exists in other markets at much wider spreads. I am aware of at least one market pair on which the DJ Mar futures is traded at different spread. The reason it makes sense to do this in futures rather than stocks is because most of the new futures have the liquidity of exiting the position assured - there is a cash settlement at the settlement date, so you don't have to worry about how you get back to cash.
For those interested, take a look at
www.sibex.com at the DEDJIA_RON Mar 10 product and then at
http://www.cmegroup.com/trading/equity-index/us-index/e-mini-dow.html. You can arbitrage as follows: say you offer at sibex at current market offer less a nominal value (just below current best offer). If lifted, you cover yourself on the Chicago market (at a lower offer). So you have to figure out how much of the Chicago product you have to buy to have a perfect hedge. This depends on 2 things: the contract size in each market and the currency exchange rate of the RON to USD. In this case, the contract size of the DEDJIA_RON is 1 RON and that of the Chicago E-mini is 5 USD. Assuming for simplicity that 1USD=1RON, for every 5 DEDJIA contracts I sold on sibex, I need to buy 1 E-mini. If the exchange rate were 1USD = 2 RON, then for every 10 DEDJIA contracts I'd need to buy 1 e-mini. (Alternatively, for every 1 DEDJIA sold, I need to buy 0.1 E-minis). All is well so far.
The problem occurs in two ways. First, the exchange rate is not an integer. Thus, it follows that the equivalence is something like this: For every 1 DEDJIA contract sold, I need to buy 0.13504567 Eminis. Problem is, I can't trade such small fractions of a contract. I think the smallest fraction is 0.1 Now, let's assume that this is really not a big deal if you trade volume, because you can always round up or down to the nearest tradable fraction of an Emini.
The second problem ad the biggest is that from trade date to settlement date there could be as much as 3 months, time in which the RON/USD rate changes. Here's the bonus question: how do you hedge this currency risk? If anyone can help, I would truly appreciate and if you have a solution that works, I'll help you set up accounts to trade on it. BTW, you do have to hold it to settlement,otherwise you'll have to exit each contract in it's own market, and thus you'll eat the bid-ask arbitrage that you just made.
Regards