The Coinmarketcap Bitcoin markets page has a special category at the bottom of the page for markets with no trading fees. Any of those markets are denoted with * to signify "Volume Excluded - No Trading Fees". The OkCoin Intl.   BTC/USD market has fees and is included in Coinmarketcap's volume calculations. The OKCoin.cn   BTC/CNY market has no fees, and is excluded. Its volume is more than ten times higher than the market with fees today.

OkCoin Intl.   BTC/USD   $ 1,341,280   
OKCoin.cn   BTC/CNY   $ 25,663,300 *

http://coinmarketcap.com/currencies/bitcoin/#markets

Any markets without fees are a joke for calculating volume from, and thankfully Coinmarketcap ignores them all.