I have yet to understand how an option contract can have such huge volume on such little open interest. At any rate the put action on UBS the other day was an extreme example of this. Looks like a lot of people are betting on UBS going down sometime soon.

P.S. I later learned that open interest is how many contracts had been written and were still open at the open of the market, and when there is a huge volume/open interest disparity it is a combination of those contracts being traded over and over, but, more likely, that many new contracts have been created that day after the market had opened buy new options writers (sellers of new contracts).