NYSE Euronext said the volume of stock trading it handled in the United States dropped again in October, after peaking in August.

The operator of the New York Stock Exchange said its average daily volume was 2.5 billion shares a day in October.

That is up 5.6 percent against October 2010. But down 2.4 percent from September.

September, in turn, was down 19.8 percent from August, when markets were highly active and NYSE Euronext had a huge surge in volume. On August 4, Standard & Poor’s downgraded U.S. debt for the first time, triggering four straight days of down-and-up 400-point swings in the Dow Jones Industrial Average. Markets stayed volatile.

For all of 2011, through the end of October, NYSE markets handled 2.3 billion shares a day. That is down 12.5 percent from 2010.

NYSE Euronext market share in trading of NYSE-listed stocks was 33.9 percent in October. That compares to 35.2 percent in October 2010 and 36.3 percent in September of this year.

Options and futures were a similar story for NYSE Euronext. Its average daily volume in derivatives, worldwide, was 8.2 million contracts. That was up 9.1 percent from a year earlier. The driver was an 18.7 percent gain in U.S. options contracts.

NYSE Arca and NYSE Amex handled daily volume of 4.7 million stock options contracts in October 2011. That was both an increase of 18.7 percent from a year earlier and a 2.0 percent increase from September.

But, globally, volume dropped 13.9 percent from the September 2011 level.

Daily volume in European derivatives was 3.4 million contracts in October. That is down 3.8 percent from a year ago and decreased 29.0 percent from September of this year.

-- This article first appeared on Securities Technology Monitor.