If it were possible for Schlumberger to look in the mirror – and it would have to be a huge mirror – it would see the biggest oilfield service company in the world. By far. Consider this chart from Spears Insiders' 2018 Oilfield Market Report:
But this is common knowledge, everybody knows Schlumberger is the biggest.  
Here are few less-well-known points:

First, notice that our firm believes that the global oilfield equipment & services market will grow to $252 billion in 2018. That is up 7% from the prior year, which itself was a growth year. The pace of growth of the SECOND year of a market uptick is always higher than the FIRST year’s growth.

Second, Baker Hughes, which is now combined with GE Oil & Gas, is about half oilfield equipment & services and half turbomachinery and controls. For this analysis we include only oilfield equipment & services. If all of BHGE was included, they would edge out Halliburton for #2.

Third, of these 6 largest oilfield service companies, 4 shrunk in 2017.  The only two that had growth? SLB and HAL. And of those two, HAL grew the most.  Seems odd to see so much retraction in a general growth year, but remember offshore was crushingly hard to navigate (pun intended) in 2017.

Fourth, when considering this list of 6, most industry observers would assume that NOV, the big capital equipment manufacturer, has fallen the most from 2014 to 2017.  And you’re right, NOV dropped about 65%. But would you be able to guess correctly who fell the second hardest in terms of sales? Schlumberger! When you rope in everything SLB does, it’s is down almost 50%.

The moral of the story: Knowing who’s biggest isn’t the whole picture, there’s a whole story in percent change. International and offshore are still big markets, but they’ve been devastated. North America is still the place you want to be for growth.