Longtime readers known that oil-services companies are among my favorite plays for long-term growth. My basic thesis is simple: The world isn’t running out of oil; it is, however, running out of easy and cheap-to-produce oil.

The recent spill in the Gulf of Mexico underscores this point. The Macondo is located in water nearly a mile deep, and the well itself was some 18,000 feet long. Such developments require an array of advanced equipment and technologies, including massive semisubmersible drilling rigs, subsea robots and devices designed to control underground well pressures. No producer would invest the time and money to produce a well of this sort if it could easily produce more oil from existing onshore fields.

That activity in these deepwater fields has picked up suggests producers must look to ever more complex and difficult-to-access fields to replace maturing fields.

Of course, it’s not just deepwater fields. Onshore fields are also becoming tougher to produce. Producers are targeting heavy oil fields that require more intensive drilling, while the unconventional oil and gas drilling boom in the US relies on technologies perfected over the past decade: horizontal drilling and fracturing.

Well complexity and service intensity go hand in hand. Each well drilled in a deepwater or unconventional field requires more work from services firms than a traditional conventional well. Services firms are the purest beneficiary of the end of easy oil.

And oil-services names are entering the sweet spot of their cycle; second-quarter results and commentary from Weatherford International (NYSE: WFT), Schlumberger (NYSE: SLB) and Baker Hughes (NYSE: BH) suggest that drilling activity will continue to pick up in the back half of the year, expanding margins further. Traditionally, these developments have acted as important upside catalysts for the group.

In the most recent live chat, a subscriber asked which oil-services stock I would buy now, Schlumberger or Weatherford International. The latter is my top pick for several reasons.

For one, Weatherford is the least exposed of the major oil services firms to a temporary ban on drilling in the Gulf of Mexico. Meanwhile, the company has a strong competitive position in Canada, Russia and Iraq–regions where drilling and production activity should increase significantly over the next few quarters. Weatherford’s exposure to North America boosted earnings in the first quarter, as activities in unconventional gas plays picked up substantially. In the back half of the year, an uptick in Russia and the Middle East should provide additional upside.

Weatherford’s stock had suffered because of a shift in Mexico’s energy policy and poor execution on some of its international contracts. But the company’s core competence in producing mature oil and gas fields is in high demand as producers and national oil companies attempt to squeeze production out of older fields.

The company’s limited exposure to the Gulf affords the firm an opportunity to outshine its peers for the first time since mid-2009, while its smaller size and attractive business footprint position the firm to grow revenue and margins at a faster rate than Schlumberger and other large competitors. Buy Weatherford International under 26.