Last week, Halliburton (NYSE: HAL) and Schlumberger (NYSE: SLB), the second largest and numero uno among the world's oilfield-services sector, respectively, along with contract driller Diamond Offshore (NYSE: DO), disclosed their results for the second quarter of 2011. In all cases, the results were strong, confirming the sentiments of those -- yours truly among them -- who are convinced that the group currently merits more than a quick once-over from Foolish investors.

Now that we're in a new week, as if to shout out to Fools still seeking an optimum spot for their investment funds amid a less-than-solid economy, Baker Hughes (NYSE: BHI) and Weatherford International (NYSE: WFT) have similarly checked in with impressive metrics. Therefore, it seems that the third- and fourth-largest of the services companies have only augmented last week's message from their larger brethren.

The baker's delicious quarter
Baker Hughes' adjusted per-share earnings vaulted to $0.93, beating analysts' consensus expectations by $0.02 but essentially moving to a different planet from the $0.23 per share that the company earned a year ago. At the same time, revenue rose 41% to $4.74 billion, versus $3.37 billion for the comparable quarter in 2010.

Geographically, international results benefited from sequential improvements in Europe, Africa, and the Russia/Caspian area. Specifically, pretax international margins -- excluding charges related to events in Libya -- expanded by 120 basis points from the first quarter of the year and ballooned by fully 675 basis points year over year.

Revenue from U.S. land sequentially more than doubled the expansion in the rig count, primarily on the basis of the heightened service requirements of the expanding list of unconventional oil and gas plays. As a result, incremental margins increased during the quarter, and the demand for pressure pumping has reached the point where it exceeds available supply. However, with Gulf of Mexico permitting occurring at a modest rate, revenue and earnings generated from that venue contributed only slight increases.

Demanding more services
According to comments from Baker Hughes President Martin Craighead on the company's post-release call, the service intensity per rig in the unconventional markets essentially results from the increased efficiency that's occurring in rig utilization and thereby leading to higher penetration rates. In addition, horizontal drilling techniques continue to improve, and the company's reservoir experts are more frequently being called upon to determine the optimum fracking techniques for efficient reservoir drainage.

CEO Chad Deaton addressed international profitability, attributing the sector's expanding margins to "solid progress toward exiting the year with mid-teen international margins. This has been a result of trimming our costs, growing our business, and improving our overall operating efficiency."

Deaton capped off his comments by noting: "The fundamentals of our business indicate that pricing should gradually improve. And we are evaluating specific markets and technologies for opportunities to raise prices, either through existing contracts or when submitting new tenders."

Weatherford plays a record
 Weatherford earned $110 million, or $0.15 per share, in the quarter, up from a loss of $48 million, or $0.06 a share, for the second quarter of 2010. Backing out one-time items, the company earned $0.17 per share, also beating analysts' expectations by $0.02. Revenues in the most recent quarter reached a record $3.05 billion, up 25% from the year-ago quarter.

Earnings for the second quarter were $0.07 above those of the first quarter, fully the result of an improvement in the international markets. Conversely, sequential results in North America were affected negatively by the severe breakup in Canada, which overshadowed strong activity in the United States.

In the Middle East, North Africa, and Asia, revenue growth was limited to 2% year over year as a result of the political unrest in the Middle East and North Africa, which was generally offset by strength in China, Australia, and Iraq. Year-over-year revenues grew by 17% in Europe, West Africa, and the former Soviet Union on strength in the North Sea, Russia, and the Caspian area. Latin America's revenues were 21% higher than in the year-ago quarter, based primarily on solid performances in Argentina, Colombia, and Venezuela.

Looking ahead to the entirety of 2011, management has raised its revenue growth projection to 25% -- versus the 20% expectation just last quarter -- and per-share earnings are expected to fall between $0.24 and $0.26.

Foolish bottom line
I'm a believer that oilfield-service companies are likely to make especially solid contributions to investment portfolios during at least the next several months. At this juncture, I'll monitor Schlumberger especially closely, including putting the company on My Watchlist. I'd suggest that you do the same.