While options trading volume and open interest stats are readily available from multiple sources, the nature of options trades remains an obscure mystery. I realize that there are two sides to every trade, but a valuable indicator would be to see the volume of trades going off at the Ask vs the Bid. A trade at the Ask would indicate Put or Call buying while a trade at the Bid would indicate Put or Call selling. Matching these metrics up with changes in implied volatility would be a powerful trading tool, in my opinion. Does anyone know of such a service, paid or otherwise that tracks this information?