Oil Discharge Monitoring Equipment (ODME) and standard oil content monitors (OCMs) are both used on marine and offshore assets to measure and control oil in water discharges but they are not interchangeable. Each was designed for a specific discharge stream, a specific regulatory standard and a specific set of operating conditions.
For FPSO projects, specifying the wrong equipment at the wrong discharge point is one of the most common and most costly instrumentation mistakes an EPC team can make.
This article explains the difference between ODME and a standard oil content monitor, sets out which discharge streams require which equipment, and clarifies when each is relevant to an FPSO project. For the broader regulatory picture, see our guide on MARPOL and FPSO compliance.
| Key thing to remember ODME and oil content monitors are governed by different IMO MEPC resolutions, measure discharge in different ways and are designed for different discharge streams. Using one in place of the other does not satisfy the applicable regulatory requirement. |
What Is a Standard Oil Content Monitor?
A standard oil content monitor also referred to as a bilge monitor, oil-in-water monitor or 15ppm bilge alarm is designed to measure the oil content of water being discharged overboard from a vessel’s oily water separator (OWS) or produced water treatment system.
Under MARPOL Annex I and IMO resolution MEPC.107(49), any vessel discharging processed bilge water overboard must do so through a type-approved oil content monitor that:
- Continuously measures oil concentration in the discharge stream
- Automatically stops discharge if oil content exceeds 15 parts per million (ppm)
- Records the discharge data for the Oil Record Book
The 15ppm limit applies to the discharge of bilge water from vessel machinery spaces after processing through an OWS. It does not automatically apply to every discharge stream on every vessel and it does not apply to tanker slop or ballast-related discharge systems.
Rivertrace’s SMART PFM 107 is an MEPC.107(49)-approved oil-in-water monitor that uses optical microscopy to differentiate oil particles, gas bubbles and solids making it well suited to produced water streams where standard bilge monitors can give unreliable readings.
What Is ODME?
Oil Discharge Monitoring Equipment (ODME) is a different category of monitoring system, governed by a different IMO regulation and designed for a different discharge application.
Under MARPOL Annex I and IMO resolution MEPC.108(49) updated by MEPC.240(65) crude oil, product and chemical tankers must be fitted with ODME to monitor, record and control the discharge of slop water, cargo tank washings and ballast water.
ODME measures discharge in different terms from a standard oil content monitor. Rather than measuring oil concentration in ppm, ODME tracks:
- The instantaneous rate of oil discharge in litres per nautical mile
- The total quantity of oil discharged as a fraction of the previous cargo (1/30,000 limit)
- The vessel’s position and speed at the time of discharge
ODME integrates with the vessel’s pumping and valve systems to automatically stop discharge if the permitted limits are exceeded. It also produces an electronic discharge record that satisfies the Oil Record Book requirement for tanker discharge operations.
Rivertrace’s SMART ODME is designed for monitoring, recording and controlling ballast and slop discharge for crude oil, product and chemical tankers, meeting the requirements of both MEPC.108(49) and MEPC.240(65).
ODME vs. Oil Content Monitor: Key Differences at a Glance
The table below summarises the main differences between the two equipment types:
| Standard Oil Content Monitor (OCM) | Oil Discharge Monitoring Equipment (ODME) | |
| Primary purpose | Monitor oil content of bilge water or produced water discharge | Monitor and control tanker slop water, tank washings and ballast discharge |
| Applicable regulation | MARPOL Annex I — MEPC.107(49) | MARPOL Annex I — MEPC.108(49) and MEPC.240(65) |
| Discharge standard | 15ppm oil content limit | 30 litres per nautical mile or 1/30,000 of previous cargo |
| Typical vessel/asset | Any vessel with machinery space bilge systems; FPSOs with produced water discharge | Crude oil, product and chemical tankers; FPSOs converted from tankers |
| Measurement basis | Oil concentration in parts per million (ppm) | Discharge rate in litres per nautical mile combined with total cargo fraction |
| Automatic shut-off | Yes — stops discharge above 15ppm threshold | Yes — stops discharge if limits are exceeded; integrates with pump and valve controls |
| Oil Record Book logging | Required for MARPOL-governed discharges | Required; ODME provides integrated electronic logging |
| Rivertrace product | SMART PFM 107 / SMART BILGE | SMART ODME |
Which Discharge Streams on an FPSO Require Which Equipment?
An FPSO may have multiple discharge streams, each governed by a different regulatory framework. The equipment required depends entirely on the stream being monitored not on the asset type as a whole.
Bilge water from machinery spaces — oil content monitor required
Bilge water accumulated in the vessel’s machinery space must be processed through a type-approved OWS and monitored by a 15ppm bilge alarm meeting MEPC.107(49) before discharge. This applies to FPSOs in the same way as any other MARPOL-regulated vessel.
Topsides produced water — specialist oil-in-water analyser required
Produced water from the FPSO’s topsides processing system is typically governed by field permits and national environmental regulations, not MARPOL Annex I directly. A specialist produced water analyser such as the SMART PFM 107 or OCD Xtra is required, not a standard shipboard bilge monitor.
For a full explanation of why produced water requires specialist monitoring equipment, see the Produced Water Discharge Monitoring for FPSOs explainer page.
Tanker slop, tank washings and ballast — ODME required
Where an FPSO has been converted from a crude oil tanker, product tanker or chemical tanker, it may retain tanker-derived discharge systems, slope tanks, cargo tank washings and ballast water systems. These systems fall under MEPC.108(49) and require ODME, not a standard oil content monitor.
This is one of the most commonly misunderstood specification points on converted tanker FPSO projects. A standard 15ppm bilge monitor installed on a tanker-derived slop or ballast system does not satisfy the MEPC.108(49) requirement and will not produce the discharge record required for tanker operations.
| Common specification mistake on converted tanker FPSOs Installing a standard oil content monitor on a tanker-derived slop or ballast discharge system in place of ODME. These two systems operate under different MEPC resolutions, measure discharge in different ways and produce different discharge records. A standard OCM does not satisfy the MEPC.108(49) ODME requirement. |
What About Purpose-Built FPSOs Without a Tanker History?
A purpose-built FPSO that was never a tanker and has no tanker-derived slope, cargo tank washing or ballast discharge systems will not require ODME under MEPC.108(49) for its topsides produced water discharge.
In this case, the applicable monitoring equipment is determined by:
- The field permit and national environmental regulations governing the topsides produced water discharge
- The process conditions oil type, concentration range, sample characteristics of the produced water stream
- Any operator or class-specific requirements applied to the project
This is why produced water monitor selection on a purpose-built FPSO is not a straightforward MARPOL compliance exercise. It requires a stream-by-stream regulatory mapping exercise before any equipment is specified.
How Does Rivertrace Help EPC Teams Get This Right?
For EPC instrumentation and process engineering teams, the ODME vs. oil content monitor question is one of several that must be resolved before procurement begins. Getting the answer wrong at specification stage creates downstream risk:
- Equipment that does not meet the applicable regulatory standard cannot be commissioned
- Late-stage specification changes affect schedule, documentation and vendor qualification
- Incorrect discharge records create regulatory exposure during port state control inspection or environmental audit
Rivertrace works with EPC teams to map each discharge stream to the applicable regulatory framework, define the correct equipment type for each stream and prepare the procurement documentation needed for technical bid evaluation.
The result is a monitoring specification that is technically correct, regulatorily defensible and aligned with the project schedule from FEED through to first oil.
Frequently Asked Questions
What is the difference between ODME and a standard oil content monitor?
A standard oil content monitor measures oil concentration in ppm and is designed for bilge water or produced water discharge under MEPC.107(49). ODME measures discharge rate in litres per nautical mile and cargo fraction for tanker slop, tank washings and ballast discharge under MEPC.108(49). They are governed by different regulations and are not interchangeable.
Does every FPSO need ODME?
No. ODME is required where the FPSO has tanker-derived discharge systems, slop tanks, cargo tank washings or ballast systems that fall under MEPC.108(49). A purpose-built FPSO without a tanker history will not require ODME for its produced water discharge, which is typically governed by field permits rather than MARPOL Annex I tanker requirements.
Can a standard 15ppm bilge monitor be used instead of ODME on a converted tanker FPSO?
No. A 15ppm bilge monitor is designed for OWS bilge water discharge under MEPC.107(49). It does not satisfy the MEPC.108(49) ODME requirement for tanker slop, tank washings or ballast discharge. Installing a bilge monitor in place of ODME on a tanker-derived discharge system leaves the FPSO non-compliant.
Which Rivertrace product is right for my FPSO discharge application?
SMART ODME is designed for converted tanker FPSOs with slop, tank wash or ballast discharge requirements under MEPC.108(49). SMART PFM 107 is an MEPC.107(49)-approved oil-in-water monitor suitable for produced water discharge, OWS discharge and drill rig applications. OCD Xtra is a produced water analyser for applications requiring calibration across multiple crude oil types. Rivertrace can advise on the correct selection at the specification stage.
When should Rivertrace be involved in the specification process?
As early as possible ideally at concept or FEED stage, before procurement and detailed engineering. Early involvement helps confirm the regulatory basis for each discharge stream, define the correct equipment type and prepare the documentation needed for procurement approval.