This study has developed a new life-of-field, goal orientated process of analysis called Holistic Environmental Assessment (HEA). HEA assesses the total environmental risk associated with a proposed oil and gas field development. It prioritises environmental risks and identifies cost effective strategies to reduce them. For the first time the process was applied to a real 'case study' field development programme to test its effectiveness. The application identified that it is a useful tool to help design eco-efficient and costeffective oil and gas field developments. Furthermore, it was discovered that much of the information required by HEA could be obtained in a quick and user-friendly format. The new assessment process was developed after a review of the interaction of the offshore oil and gas industry with the environment, and techniques employed to evaluate this interaction. The review identified that the industry interacts with the environment in a number of different ways, and that the level of interaction transgresses the boundaries of sea, air and land locally, regionally and internationally. Legislation and public concern demand no damage to the environment from offshore oil and gas field exploration and development. UK environmental legislation and people's expectations for environmental performance are in a state of change. This change, coupled with the uncertainty over how resilient the environment is to perturbation, and the increasing risk of environmental liability presents a need for operators to clearly manage environmental information and assess total environmental risk. It was discovered that Environmental Assessment, Lifecycle Analysis and Cost Benefit Analysis, when used separately, failed to assess total environmental risk, but when used in combination under the HEA process could. Many organisations, such as the British Medical Association, European Oilfield Speciality Chemicals Association, the Royal Ministry of Petroleum and Energy (Norway) and Shell Expro, now recognise that a holistic approach is essential to assess total environmental risk. The author proposes that HEA would be effective as a software tool to analyse different environmental risk mitigation systems. This would facilitate the identification of a system that steers an operator towards the triple bottom line of Sustainable Development.