Just when it seemed likely that futures trading on the box office performance would become as commonplace as futures trading on corn and oil, a Senate committee has stepped in to prevent such trading from materializing. In a surprise action that was hailed by movie studios and exhibitors, the Senate Agriculture Committee -- of all entities -- voted to adopt an amendment to the Wall Street Transparency and Accountability Act that would bar futures trading on movie ticket sales. The Senate committee has regulatory oversight on the futures exchanges. The action comes as a blow to the global financial services company Cantor Fitzgerald and an Indiana start-up, Media Derivatives, who had received preliminary approval from the Commodities Future Trading Commission to create the box-office exchange, but its assent represented only a first-stage action, and some members of the commission have already indicated that they are skeptical of the proposed exchanges. The Senate bill still faces a lengthy legislative process before it winds up on President Obama's desk.