We investigate the relations between trading volumes and our proxies for information flows and divergences in opinions. We view S&P 500 Index futures' open interest as a useful proxy for divergences of traders' opinions, and find that volumes are higher on days when open interest increases than on days with declines. Volume in individual equities is more closely related to firm-specific information flows, while equity basket volume is more closely associated with market information. This differential impact is greatest for small capitalization stocks where market-wide news has no explanatory power.