In the first half of 2011, the Big Four benefited from tight supply-demand conditions for many key services, as frenzied drilling activity in North American shale oil and gas plays strained the industry’s capacity to meet these needs.

In particular, a shortage of pressure pumping capacity–a service critical to hydraulic fracturing–had enabled service providers to push through substantial price increases in recent years.

Hydraulic fracturing is a process whereby producers pump a…