The document provides a summary of derivative market activity in India for July 18, 2011. Key points include: - Nifty futures open interest increased 0.67% while Mini Nifty increased 3.48% as the market closed at 5581.10 - Nifty July futures closed at a premium of 5.85 points and August futures at a premium of 22.60 points - Implied volatility of at-the-money options decreased from 18% to 17.3% - Total open interest in the market was Rs. 135,158 crore with stock futures open interest at Rs. 34,675 crore.