In the case of these three companies, you could say their Achilles' heel is that they are all more dependent on higher oil prices than many others in the space. Atwood generates 73% of its revenue from its fleet of high-specification rigs for ultra-deepwater drilling, a majority of National Oilwell Varco's revenue come from the manufacturing of drilling packages for offshore rigs and the aftermarket replacement parts, and Denbury Resources' enhanced oil recovery process involves lots of up-front capital to inject CO2 into older oil fields.