In this article, the authors examine the potential effects of a Commodity Transaction Tax (CTT) on commodity and futures markets. They investigate the relationship between bid-ask spreads, trading activity, and intra-day volatility using futures data on five commodities (gold, copper, crude oil, cardamom, and refined soya oil) from 2006 to 2010. The empirical results suggest that while higher transaction costs may decrease trading activity, they may also increase price volatility. Therefore, policy makers should pay close attention to the possibility of distortions in market microstructure should a CTT be imposed in India.