The May US Services Purchasing Managers' Index conducted by Markit came in at 56.8 percent, up 2.2 from the final April estimate of 54.6. The consensus was for 55.7 percent. Markit's Services PMI is a diffusion index: A reading above 50 indicates expansion in the sector; below 50 indicates contraction.

Here is the opening from the latest press release:

According to the latest survey data, business activity increased at a sharp rate across the U.S. service sector in May. Although the pace of new business growth softened slightly, it remained among the fastest in the last three years. Backlogs of work meanwhile accumulated at the quickest pace in over three years, prompting companies to boost capacity by upping the rate of job creation to the strongest since September 2015. The survey also showed rates of both input cost and selling price inflation accelerating. [Press Release]

Here is a snapshot of the series since mid-2012.