The "White Knuckler" of the 2012 - The Express Scripts-Medco deal had some tense moments. As did the aforementioned GILD-VRUS deal. (And don't forget Dollar Thrifty/Hertz Global Holdings.) But for sheer tension, nothing matched what arbs playing the Nexen (NXY) deal felt on the afternoon of 7 December. That, of course, was the day Canada was either going to bless NXY's deal to be acquired by CNOOC or reject it. With plenty of potential upside and downside riding on the binary outcome, waiting for that decision must have been a stressful few hours for many of the world's biggest merger arbitrage desks.