Marine oil spill risk assessment

On this page we provide information on the Marine Oil Spill Risk Assessment (MOSRA) model and how it has been used to help to determine the way that the Oil Pollution Levy (OPL) is allocated to the different sectors that pay the levy.

The MOSRA 2018 report and the MOSRA 2015 report (including its annexes), are available at the links below:

Marine Oil Spill Risk Assessment (MOSRA) summary report 2018 [PDF: 359kB, 4 pages] Marine Oil Spill Risk Assessment (MOSRA) report 2015 [PDF: 7Mb, 397 pages]

Also available is the interactive MOSRA model which you can explore. The model is at the following link:

MOSRA online modelling [Navigatus Consulting website]

Web based visualisations are available for coastline and sea areas on matters such as risk, navigational hazard, environmental factors and oil sources. Selecting individual ‘cells’ will allow you to see more detail around the factors considered in the model for that cell.

Please log on as a “Guest” and please allow time for the model to load (this may take a little while due to the complexity of the model and the volume of data involved).



Maritime New Zealand is a key player in the regulatory, compliance and response framework that is designed to manage the risk of marine oil pollution, and ensure that New Zealand is prepared to respond effectively to oil spills that occur in the marine environment.

Internationally, New Zealand is a signatory to a number of conventions relating to oil spill liability for those operating in the marine environment. New Zealand is also a signatory to the Oil Preparedness, Response and Co-Operation Convention which enables us to call on other signatories to assist in the event of a major marine oil spill.

The national framework for marine oil spill prevention, preparedness and response activities includes the Maritime Transport Act 1994, the Resource Management Act 1991, the Health and Safety at Work Act (HSWA) 2015, the Hazardous Substances and New Organisms Act 1996, and the Exclusive Economic Zone and Continental Shelf (Environmental Effects) Act 2012.

The cost of oil pollution preparedness is met by operators in the maritime sectors either directly or through the Oil Pollution Fund (the Fund). The Fund is financed by the Oil Pollution Levy (the Levy), which is paid by the commercial maritime industry - those who use oil as fuel, transport oil, and the offshore oil industry. These levy contributions enable Maritime New Zealand to operate the Marine Pollution Response Service (MPRS) and to deliver associated regulatory and compliance services.


Risk assessment and the MOSRA process

Maritime New Zealand uses a risk assessment approach to consider both the likelihood and the consequence of a marine oil spill occurring. Since 1992 we have been using a formal risk study process – the Marine Oil Spill Risk Assessment or MOSRA to do this. Over the years the MOSRA has been extensively developed and evolved to incorporate the best possible statistical data and the latest techniques and practices in modelling and analysis. We use the MOSRA to help us to decide what readiness and response capabilities are appropriate and what we need to do to deliver the National Marine Oil Spill response Strategy.

Sector analysis and risk allocation

Since 2015 we have also used the MOSRA work to determine the share of the overall risk that should be allotted to each of the contributing maritime sectors. The MOSRA process looks at risk in terms of likelihood (probability) and consequence and uses both domestic and international data. International data is necessary due to the very small sample sizes for New Zealand based activity. The MOSRA then takes these results and for the sector share analysis considers the relative risk between sectors i.e. which sector has the greatest risk when compared to the other sectors.

We ensure that the model uses the latest technical developments and the latest available accident and incident statistics for shipping, the latest vessel tracking and routing information and data on the types and volumes of oil carried to and from and around New Zealand.

MOSRA model development

The table below shows how we have developed the modelling over the years to the present day.

First national risk assessment undertaken to inform first marine oil spill response strategy.
Based on 1992 model. Addressed possibility of catastrophic spill.
Built on the 1998 model. Refinements made to model to improve reliability and cater for improved data input.
Built on the 2004 model. Improvements included web interface, ability to change input factors, environmental data and risk.
Built on the 2010 model. Improvements include offshore impacts, integration of sector analysis into model, and different impacts of different oil types.

The MOSRA 15 study is a significant step forward from the work in 2010.  Using the latest statistical modelling techniques it provides an accurate picture of New Zealand’s current oil spill risk profile with the following key features:

  • Accounting for various types of oil (floating, sinking, dissolving):
  • Enabling sensitivity analysis to reveal the relative importance of maritime factors and modelling assumptions;
  • The ability to 'look ahead' to reveal the effect of known trends as well as a range of credible future risk profiles and to enable trends and future changes within and across sectors to be explored;
  • Reflecting current environmental values for spilt oils at the coastline and away from the coast, whether from vessel incidents, routine production activity, or exploration activity;
  • Modelling of existing, planned future and various potential off shore activity (in the form of scenarios or as a continuum);
  • Enabling sector contribution to be determined across sectors for levy collection purposes (as part of its core capability) and for this to be updated from time to time;
  • Assessing latest environmental information such as marine mammal protection areas, new research findings and advice from experts;
  • Furnishing relevant information (overview and drill down) for oil spill response planning functions (similar to MOSRA 10).



MOSRA 18 is a refresh of MOSRA 15. Large vessel activity has been brought up to date and modelling of routing refined. A greater level of details has been available for domestic tanker activity and also for the types and volumes of oil carried.

The key factors that were considered and included in the update include:

  • Vessel activity and routing,
  • The proportion of oil types carried,
  • Assumptions regarding standards of pilotage across each large vessel sector, ferry schedules and, for tankers, full compliance with IMO Regulation 13G (double hulls and bunker protection).