The Chicago Board Options Exchange garnered the most options volume of all six options exchanges in July, but its lead over archrival International Securities Exchange shrank to 4.7% from 8.4% in June. The hybrid exchange attracted 34.4% of all options volume in July, down from 36.9% in June. The all-electronic ISE's market share grew to 29.7% of all options volume in July from 28.5% in June, according to the Options Industry Council. Bruce Goldberg, ISE chief marketing officer, attributed growth in ISE's volume to a variety of different factors, including improving quality of execution and liquidity, but said no particular event bolstered its volumes. The Philadelphia Stock Exchange continued to add volume to rank third amongst rivals, growing its market share of all options traded to 12.6% in July from 12.2% of in June. The American Stock Exchange remained in the fourth place. Its market share slipped slightly to 9.5% in July from 9.8% in June. NYSE Arca, while still in fifth place, grew its market share slightly to 8.8% of all options volume from 8%. Some traders speculated Arca will be able to grow its market share even faster now with its newly revamped low-cost options trading platform, due to launch later this month. Indeed, over the last two weeks in July and into August NYSE Arca was pulling double digit volumes more than occasionally. The Boston Options Exchange, in last place, grew its market share to 5% of all options volume from 4.7%.