Following the April 2010 Gulf of Mexico (Macondo) oil spill and the 2009 Montara incident in Australia, the International Association of Oil and Gas Producers (OGP) formed the Global Industry Response Group. This Group identified nineteen oil spill response recommendations (OGP, 2011) that are being addressed via an Oil Spill Response Joint Industry Project (OSR-JIP) during 2012–2014. The OSR-JIP is managed by IPIECA on behalf of OGP, in recognition of IPIECA's long-standing experience with oil spill response matters.

One of the nineteen recommendations concerned the development of an international guideline for offshore oil spill risk assessment and a method to better relate oil spill response resources to the risk level. Consequently, the OSR-JIP has published a guideline covering oil spill risk assessment and response planning for offshore installations.

This paper describes the development and content of the guideline, including how the oil spill risk assessment process provides structured and relevant information to oil spill response planning for offshore operations. The process starts by defining the context of the assessment and describing the activity to be assessed. Thereafter it addresses a series of key questions:

  • What can go wrong, leading to potential release of oil?

  • What happens to the spilled oil?

  • What are the impacts on key environmental - both ecological and socio-economic - receptors?

  • What is the risk for environmental damage?

  • How is the established risk utilised in oil spill response planning?

The guideline draws on existing good practices in the determination of oil spill response resources. It promotes consideration, in tactical and logistical detail, of the preferred and viable response strategies to address scenarios covering the range of potential oil spills up to the most serious. The methodology to evaluate the potential spill scenarios utilizes a series of questions:

  • What are the viable techniques/strategies to deliver response with greatest net environment benefit?

  • What are the tactical measures required to implement the identified response strategies, considering technical, practical and safety factors?

  • What Tiered resources are required to mount the tactical measures and achieve effective response?

The paper summarizes the useful tools, key information and the necessary level of detail essential to perform an oil spill risk assessment for use in oil spill response planning.

The oil and gas industry recognizes the importance of assessing the oil spill risks associated with its operations and implementing measures to manage these risks. The primary focus and priority is the reduction of risk by the prevention of incidents which may lead to oil spills. However, additional risk reductions can be achieved by ensuring an effective incident response through the establishment of source control (e.g. well killing, well capping and containment solutions) and oil spill preparedness measures.

Following the April 2010 Gulf of Mexico (Macondo) oil spill and the Montara incident in Australia, the International Association of Oil and Gas Producer's (OGP) Global Industry Response Group identified 19 oil spill response recommendations that are being addressed by the 2012–2014 Oil Spill Response Joint Industry Project (OSR-JIP). The OSR-JIP is managed by IPIECA on behalf of OGP in recognition of its long-standing experience with oil spill response matters.

International harmonization of methods for oil spill risk assessment and preparedness planning was one of the recommendations from the group. Working through the OSR-JIP, IPIECA and OGP have developed and published a guidance document on oil spill risk assessment and response planning (IPIECA and OGP, 2013). It is a tool to enhance the industry's offshore oil spill prevention and preparedness efforts and to better communicate those efforts to the various stakeholders. The guidance document applies to all offshore oil and gas units and infrastructure. Spill from marine transport and consented releases of liquid hydrocarbons are not covered by the guidance. The guidance document and this paper are structured in two related parts; (1) oil spill risk assessment (OSRA) and (2) oil spill response planning.

One of the working groups under the OSR-JIP was the “Oil Spill Preparedness Work Stream” with a steering committee of 12 industry representatives, which defined the scope of work for the guideline development and provided technical input and review of the guideline.

Two consulting companies were appointed to undertake the work - each focusing on either Part 1 (oil spill risk assessment) or Part 2 (response planning). Two face-to-face meetings with the steering committee were held during the drafting and review process, backed-up by a number of teleconference and written comments. This process ensured that existing industry consensus and good practice was embedded into the guidance document, as well as the lessons learned post 2010. The interest from the steering committee in the guidance was very high, with many comments being offered throughout the drafting process. The guidance was aligned with related work areas, including references to the new capping and containment capabilities, and the development of other oil spill planning documentation (API, 2013).


The oil spill risk assessment (OSRA) addresses the likelihood of liquid hydrocarbon releases to the sea and their potential for ecological and socio-economic consequences. The guideline covers the process of planning and executing the OSRA, and includes recommendations on how to analyse and evaluate the risk. The elements of the OSRA process are illustrated in Figure 1.

Oil spill risk assessment context

The OSRA will often be part of an overall risk assessment process for safety, environment and assets. It starts by defining the context of the assessment and describing the activity to be assessed. The main objective of conducting an OSRA is to determine that the offshore activity is in line with corporate risk tolerance and provide input to the Oil Spill Response Planning.

The OSRA shall identify and evaluate the risk to the environment, from accidental oil spills from offshore units. Ecological and socio-economic risk tolerance criteria (RTC) should be established prior to the start of the OSRA as they constitute a baseline for the evaluation of the results from the risk assessment. The risk level should be evaluated against these ecological and socio-economic RTC as well as the ALARP principle (As Low As Reasonable Practicable principle). RTC is defined by the maximum likelihood of a given consequence that is tolerable for the operating company.

Hazard identification

For the purpose of the OSRA the focus during hazard identification should be on events related to the potential releases of liquid hydrocarbons to the surrounding environment (Figure 1). The hazard identification process should be as comprehensive as reasonably practicable; events which are identified as hazardous will form the basis for subsequent analyses and the selection of oil spill scenarios.

Likelihood analysis and scenario selection

The objective of the likelihood analysis is to characterize the identified hazardous events, in terms of likelihood, event duration and location, potential volumes of hydrocarbons discharged, and the type of hydrocarbon released.

The degree of detail to be achieved for the likelihood analyses will depend on the type of OSRA to be carried out: a high degree of detail and use of statistics based on relevant historical events would typically be required for a quantitative analysis, while less detail would be required for a qualitative analysis. When all hazardous events have been identified and characterised, an assessment is undertaken to select those events to be taken forward in the OSRA and to define the oil spill scenarios to be modelled. The oil spill scenarios are then analysed through fate and trajectory modelling to determine potential consequences, which are combined with the event's likelihood to establish the risk (Figure 1).

All the identified hazardous events may be considered for further analysis but, as a minimum, all events that potentially have a significant contribution to the risk should be considered. At this stage in the OSRA there is no detailed information concerning the possible environmental consequences of the identified hazardous events. However, experienced risk assessors or local environmental specialists will be able to make an initial estimate which events may have the potential for high consequences.

The aim of the selection process is ultimately to provide a risk basis for oil spill response planning. This planning is typically structured as a tiered response (see Part 2: Response planning; Figure 1). It is recommended that, in selecting oil spill scenarios, consideration is given to ensure that all three of the response tiers are covered. Figure 2 provides an example of how release scenarios are selected from hazardous events, presented in terms of their likelihood and quantity of oil spilled. This example considers a floating production storage and offloading unit (FPSO) with subsea production wells and export through offloading. Sixty-four hazardous events have been identified (combination of a source, quantity and a release position).

International subsea capping and containment capability will be relevant risk reducing measures in case of a loss of well control (blowouts), which can have an effect on the likelihood of the release durations. Thus, capping needs to be taken into account during the likelihood analysis and scenario selection.

Consequence analysis

For each of the selected release scenarios, the potential environmental consequence is combined with the likelihood of oil pollution to establish the risk. In this context, environment refers to both ecological and socio-economic resources. The determination of a consequence value requires four steps:

  1. identify possible oil pollution in marine and coastal areas through modelling of the fate and trajectory of spilled oil;

  2. identification & characterization of potential environmental receptors at sea and on shorelines;

  3. evaluation of the sensitivity of the environmental receptors, and identification of those to be used as impact indicators for the determination of consequence values, and

  4. assessment of environmental consequences as a function of oil exposure and environmental sensitivity.

1) Fate and trajectory modelling

The objective of computer simulation of oil spill fate and trajectory is to estimate the physical changes which spilled oil undergoes (i.e. weathering processes) and its potential pathways, travel times, areal distribution and associated volumes under the prevailing wind and current conditions. The applied oil spill model should be relevant for the spill scenarios and be able to cover both a subsea and topside oil release.

An oil spill trajectory model should use wind and three dimensional current data based on in-situ monitoring and/or modelled oceanographic or meteorological data fields. The data should cover all seasons and be specific for the region where the offshore activity will take place. The oil spill modelling should be stochastic, allowing for a large number of simulations based on variations in historical wind and current data. The modelling should ensure sufficient number of spill simulations to reflect the variations in the metrological and oceanographic input data. The stochastic analyses should be paired with the most relevant deterministic cases that can be utilized to support response planning.

The modelled fate and trajectory of the spilled oil may be presented as maps and tables showing the probability of the distribution of oil both at sea and on shorelines. Single (deterministic) simulations may be presented in maps with oil movement over time, see examples in Figure 3. The limitations and resolution of the modelling should be understood and documented together with the quality of input data.

2) Identification of ecological and socio-economic resources

Mapping of ecological and socio-economic resources allows the identification of the resources that can be exposed to oil. Mapping should be performed within the influence area of the potential spills including both open sea and coastline. It should include spatial and temporal distribution and sensitivity of the resources at a relevant scale. The objective is to capture significant temporal or spatial variations in the potential environmental consequences as inputs into the risk assessment and oil spill response planning.

3) Evaluation of sensitivity of ecological and socio-economic resources

The evaluation and ranking of the sensitivity of environmental resources aims to address their ability to tolerate and recover from acute exposure to oil during a spill. There are three main elements to consider when ranking the sensitivity of the environment to oil:

  • Sensitivity of biological features: This is a species- or group specific sensitivity that is a combination of individual sensitivity to oil pollution (e.g. toxicity, smothering effects, behavioural pattern that affects the likelihood to be exposed to the oil pollution) and the population's sensitivity to disturbance in terms of its recovery ability.

  • Shoreline sensitivity: This describes the different shoreline substrates holding capacity for oil, and how effectively it is cleaned by natural mechanisms.

  • Socio-economic sensitivity: Socio-economic sensitivity is derived from the economic importance of the resource (e.g. fisheries, recreational beaches, marinas etc.) and the likelihood that oil pollution will have an impact on the socio-economic activity in the event of a spill.

The above three elements should all be taken into consideration when ranking the sensitivity of the environment in the influence area and defining the impact indicators. This means that a limited number of the most sensitive ecological and socio-economic resources in the influence area are selected, and used to categorize or quantify the consequences.

4) Assessment of environmental consequences

Assessment of the potential ecological- or socio-economic consequences may be qualitative or quantitative, depending on the availability of information. The assessment should, as a minimum, be based on the sensitivity of the impact indicators and the potential exposure to oil pollution. A qualitative consequences assessment can be expressed as a relative ranking of consequences; for example as a relation between the Environmental Sensitivity Index (ESI) and the estimated oil amount or oil concentration that can pollute the area. A more detailed assessment of consequences can be performed based on established relations between oil exposure volumes or concentrations and the effect on the impact indicators such as shoreline habitat, seabird populations, sea turtle populations or fisheries. Such quantitative relations can for example be expressed as a relation between the extent of oil exposure (volume/concentration), the effects of the oil in terms of ecological damage or economic loss, and the potential duration of the environmental impact in terms of recovery time.

Establishing and evaluating the risk

Risk is established by combining the likelihood and the potential consequence of each scenario. Once the risk has been established, the primary objectives are to evaluate and communicate the risk of an activity or scenario to stakeholders and decision makers in a logical and understandable way to secure that the risk level is tolerable and that properly informed decisions can be made regarding the implementation of risk reducing measures to achieve a risk level that are as low as reasonably practicable (ALARP). Use of the ALARP principle is recommended for all activities included in the OSRA. The principle is that activities not meeting risk tolerability criteria shall be subject to risk reduction regardless of cost, and that the residual risk is tolerable provided that it is as low as reasonably practicable.

A clear and balanced picture of the risk exposure should be presented by giving the likelihood for different consequences or consequence categories resulting from the oil spill scenarios and activities. The risk may be presented for different environmental compartments (e.g. sea surface, water column, shoreline etc.) and for the various socio-economic resources or activities. The main focus should be on the impact indicators with the highest risk level.

Figure 4 presents an example of a coarse risk assessment with the consequence assessed in a matrix as the relation between oil amount potentially affecting impact indicators and the sensitivity of the impact indicators. The consequence level is thereafter combined in a risk matrix with the likelihood of the oil spill scenarios, which is the combination of likelihood of an oil spill and the probability for exposure of the impact indicators (results from the oil trajectory modelling).

The risk presented by the oil spill scenarios should be evaluated against risk tolerance criteria (RTC) or other environmental decision criteria/goals. Depending on the outcome of the risk level evaluations, it may be necessary to take measures to reduce the risk. Risk tolerance criteria define the threshold for a tolerable likelihood of an environmental impact. The tolerable threshold varies with the severity of the environmental impact, where higher likelihood is tolerable (acceptable) for less severe consequences. This is indicated in the risk matrix in Figure 4, where the high consequences events are not tolerable or in the ALARP area, even if the likelihood is low, while low consequences events can be tolerable also when the likelihood is higher.

Input to oil spill response planning

For the purposes of oil spill response planning and determining oil spill response capability, the results from the OSRA will provide important input related to the likelihood of different spill scenarios, the ecological and socio-economic consequences of the scenarios, and the likelihood of exposure and oil volumes in geographical areas. As discussed in Part 2 of this paper, such information supports the strategic selection of key scenarios for further analysis in response planning, including Net Environmental Benefit Analysis (NEBA), establishing response strategies and assessing resource needs across all response tiers. During the selection of oil spill scenarios consideration should be given to ensure that all three response tiers are covered. Typically this may involve one or two scenarios commensurate with each of the three oil spill response tiers. As a minimum, the oil spill scenarios representing the highest risk to the environment should be included in the oil spill response planning. If the risk level of the activity is high, more detailed oil spill response planning is warranted.

Response planning considers, in tactical and logistical detail, the preferred and viable response strategies proposed to address the representative oil spill scenarios identified in the OSRA. It should be used as the basis for the determination of appropriate oil spill response resources at each Tier and thereby demonstrate that preparedness is commensurate and balanced with the risk posed by an offshore installation. The response planning process is shown in Figure 5 and addresses the following questions:

  • What oil spill scenarios are identified in the OSRA?

  • Do all the scenarios warrant detailed analyses for the determination of oil spill response resources at each response Tier?

  • What are the viable strategies for delivering a response with the greatest net environment benefit, for the scenarios subjected to detailed analyses?

  • What are the tactical measures required to implement the identified response strategies, considering technical, practical and safety factors?

  • What Tiered resources are required to mount the tactical measures and achieve an effective and realistic response?

The guidance recommends that a scenario response planning team is formed to undertake the response planning process. This team should involve persons with knowledge and experience of the operations associated with the offshore installation; the OSRA; the principles of oil spill contingency planning and response options; logistical capabilities and constraints; the relevant legislative framework; and stakeholder/public factors which may affect response options.

Relatively few scenarios may warrant detailed analyses to determine the extent of required response resources at each of the three Tiers; typically one or two scenarios from each Tier will be sufficient. In some cases, it may be adequate to consider a single scenario covering the worst credible case discharge (WCCD1), as this will involve the escalation of a response through all three Tiers.

The response planning team is responsible for ensuring that the scenario(s) identified by the OSRA covers the potential range of realistic oil spill challenges posed by the offshore installation throughout the period of operation, up to the WCCD. The response planning should be realistic and thorough enough to determine, demonstrate and verify that overall oil spill preparedness is commensurate with the risk. The substantial work of the scenario response planning team revolves around the analyses of the scenarios. Each of the scenarios should be subject to detailed consideration of anticipated response actions, incorporating a variety of elements, which are detailed within the guideline.

Response requirements and the determination of response resources

The output from the analyses of the chosen scenarios is a set of strategic, tactical and logistical requirements which Tiered response resources will need to fulfil. The determination of these resources should encompass the type, quantity, location and mobilization times of equipment and the organizational framework for effective incident management, including trained personnel and procedures for the integration of different organizations into the overall response effort. The guideline gives detailed examples of tactical planning at the three Tiers. This illustrates how the process can be undertaken and documented.

Consolidation of output from the detailed tactical planning for each scenario provides information concerning the overall equipment, logistics and personnel resources required to implement the identified tactics. The response planning team should evaluate the resources currently available to the operation at each Tier, including the times for their mobilization and deployment within the theatre of response operations. Reduction in capability due to potential prevailing seasonal and climatic conditions should also be considered. This allows gap analyses to identify whether the existing resources and their associated logistics are either adequate or require alterations or expansion, as illustrated in Figure 6. A variety of potential actions arising from the Resource Gap Analyses are included in the guidelines.

Comprehensive and coordinated incident management is fundamental to effective response. Therefore the guideline also emphasises the need to consider and establish an incident management organization utilizing a Tiered approach in oil spill contingency plans. The key elements of effective incident management are outlined.

Organizational structure and procedures based on the Incident Command System (ICS) are widely adopted by the international oil industry. The use of ICS-based incident management may serve as a reference, as the approach addresses the key elements listed above. Furthermore, an aligned and consistent approach to incident management can facilitate integration of external organizations supporting the response effort. The guideline stresses the need for relevant training and exercising programmes for personnel in allocated roles within the incident management system, and provides information concerning relevant programmes.

It is important that the interface and integration between an offshore installation's incident management capability and relevant government agencies are considered. In the case of Tier 2 or Tier 3 incidents, it is likely that the government will be involved in various aspects of the response, including the facilitation of regional or international support. In those countries where the International Convention on Oil Pollution Preparedness, Response and Co-operation (OPRC Convention) is ratified and implemented, the country's national plan should stipulate an overall framework for incident management. Specific guidance for offshore operators may be established in these cases.

In those countries where the OPRC Convention is either not ratified or not fully implemented, it is recommended that clarity on national policy concerning the key incident management elements is sought from relevant authorities. Where the authorities utilise an organizational structure at variance with an operator's internal system and procedures, the operator should identify and document this within their oil spill contingency plan. The guidelines provide information concerning cooperation and mutual aid between operators, recognising that oil companies commonly practice cooperative approaches to establishing and sustaining oil spill response resources at Tier 2 and Tier 3.

Assessment of preparedness

The guidance recommends assessment of oil spill preparedness, in situations where:

  • there is a need to check if a draft contingency plan has addressed required elements;

  • verify a finalised plan and its related procedures are fit for purpose;

  • confirm the preparedness measures and response capacity, including the incident management team, are as stated in the plan;

  • provide periodic review of a plan.

An example of the basic process steps that an assessment could follow are contained in the guidelines. There are also specific tools to support oil spill preparedness assessments available (ARPEL, 2012 and IMO, 2010).

The primary focus of oil spill risk management for offshore installations is on preventive measures. However it is recognised that well intervention, capping and containment, and oil spill preparedness measures can also make further important contributions to risk reduction and meet societal expectations relating to environmental protection. Against this background - and addressing one of the Global Industry Response Group's 19 recommendations relating to oil spill response - a guideline for oil spill risk assessment and response planning for offshore installations has been developed and published through the IPIECA-OGP OSR-JIP.

In the development and drafting of the guideline, existing good practice was captured and inputs sought across the OGP and IPIECA memberships, through the relevant OSR-JIP Work Stream. The resulting document is a comprehensive guideline covering the process of oil spill risk assessment and how the outputs from such assessments can be used for the planning and determination of required response resources.

Guidelines for Offshore Oil Spill Response Plans: Guidance for Offshore Oil and Gas Exploration, Production and Pipeline Facility Operators
API Technical Report 1145. Available at
Oil Spill Response Planning and Readiness Assessment Manual (RETOS)
Available from
Manual on Oil Spill Risk Evaluation and Assessment of Response Preparedness
IMO Publication I579E, ISBN 978-92-801-1512-3
Guidance Document on the Implementation of an Incident Management System (IMS)
IMO Publication I581E, ISBN 978-92-801-1553-6
Finding 6: Oil spill risk assessment and response planning for offshore installations, Final Report
. .
Oil spill response - Global Industry Response Group recommendations
International Association of Oil & Gas Producers report number 465. Available from

1The WCCD case scenario sets the upper limit for a sustained Tier 3 response. This scenario can be interpreted as the largest release that could reasonably be expected from a facility or operation. If no national/regional requirements provide definitions of the WCCD it is recommended that the WCCD is defined based on the worst credible consequence scenarios.