But still playing catch-up in U.S. market share, according to Nielsen’s August survey

Click to enlarge. Source: The Nielsen Company

The chart at right, released Tuesday, speaks for itself.

Google’s GOOG Android was the most popular operating system in the U.S. among customers who purchased smartphones within the past six months, according to the Nielsen Company’s August survey.

The same survey found Apple’s AAPL iPhone and Research in Motion’s RIMM BlackBerry in a statistical tie for second place. As Daring Fireball‘s John Gruber points out, the numbers are very different in Europe, where the iPhone is available on multiple carriers in most countries.

In Nielsen’s most recent chart of the shifting U.S. smartphone market shares, BlackBerry was still No. 1, with the iPhone creeping closer and the army of Android phones marching at double time.

Source: The Nielsen Company

[Follow Philip Elmer-DeWitt on Twitter @philiped]