This book analyzes the safety of drilling operations with regard to the prevailing pressure regimes. Quantitative risk assessment is conducted for the stages of drilling operations – drilling ahead, tripping, casing and cementing. A diagnostic model for analyzing the rotating control device, the main component of managed pressure drilling techniques, is developed. The unique relationship between casing and cementing operations in leading to well integrity failure is modeled while utilizing relevant safety functions and inherent safety principles to improve the operations. Loss function modelling approach to enable dynamic consequence analysis is implemented to study blowout risk for real-time decision making. The aggregation of the blowout loss categories, comprising: production, asset, human health, environmental response and reputation losses leads to risk estimation using dynamically determined probability of occurrence.