SAN FRANCISCO May 1 (Reuters) - CBOE Holdings Inc said trading on its flagship Chicago Board Options Exchange fell in April, as the oldest U.S options exchange gave up market share to rivals.
Trading at CBOE fell 6 percent to a daily average of 4.01 million contracts, the Chicago-based company said in a statement on Wednesday.
A software bug prevented CBOE from opening for half the day last Thursday. But the decline was bigger than could be blamed on business lost on that single day.
Trading at all 11 U.S. options exchanges, including CBOE and a smaller CBOE-owned electronic exchange known as C2, rose 6 percent to a daily average of 16.9 million contracts, options clearinghouse OCC said earlier on Wednesday.
CBOE's market share fell to 24.2 percent in April, down 1.7 percentage points from the prior month, the exchange said.
CBOE did not provide a reason for the decline, but activity typically suffers in tranquil markets like those seen in April.
CBOE's Volatility Index, better known as Wall Street's fear gauge, last month stayed well below its long-term average of just over 20.
Cushioning the blow to CBOE profits was a 26 percent rise in April trading of CBOE's stock-index options, its most lucrative products because they are licensed to trade exclusively at CBOE.
The company also noted the month marked a record for its secondary C2 exchange, which handled 399,000 contracts a day in the month and accounted for a 2.4 percent of all trading on U.S. stock-options markets, more than twice its 1.1 percent market share a year earlier.
CBOE releases its first-quarter results on Friday.