The May US Services Purchasing Managers' Index conducted by Markit came in at 53.6 percent, up 0.5 percent from the April estimate. The consensus was for 54.1 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:

Growth of business activity in the US service sector accelerated slightly in May, reaching a three-month high. This extended the current period of activity growth to 15 months.

The seasonally adjusted Business Activity Index continued to run above the crucial 50.0 no-change mark during May. A reading of 53.6, up from 53.1 in April, signalled the largest rise in overall activity since February. [Press Release]

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

Markit Services PMI