<p>In oil well drilling operations, Loss of Well Control (LOWC) can result in catastrophic event like Blowout that can adversely affect man, material and environment. Hence, well control is imperative to uphold well integrity during entire operational processes by means of primary and secondary well control barriers. Failure of primary and secondary well control barriers can result in Blowout whose occurrence probabilities during drilling process of developmental well operations are discussed in past literature. The present study aims at risk assessment of causes influencing LOWC among wildcat, exploratory and developmental wells during drilling, completion, production, workover and wireline operational phases. In addition to occurrence probabilities of these factors, severity and non-detection probabilities are also estimated. Major causes derived from SINTEF database are used to develop a Bayesian Network (BN) model for Blowout scenario. The prior probability of LOWC causes are obtained using expert elicitation process. The posterior probabilities of causes are estimated based on Bayes’ theorem principle. The results of Quantitative Risk Analysis (QRA) and criticality analysis are then validated with International Oil and Gas Producers (IOGP) database. It is concluded that the results obtained from the study are in accordance with database value such that Blowout probability and critical causes vary among different wells. Risk assessment of causes influencing LOWC is performed and measures to prevent occurrence of well control incidents are proposed.</p>