LAUF Fugitive Emissions Calculator

What is LAUF?

LAUF (Lost And Unaccounted For gas) is a term used by natural gas (methane) distribution utilities and regulators to refer to leaked gas. These utilities purchase gas that comes from transmission pipelines and pump it through pipes to homes and businesses. LAUF is the difference between the amount of gas purchased from the transmission companies and the amount sold to the homes and businesses.  Every year, each of these utilities in Massachusetts submits a report to the MA Department of Public Utilities detailing their lost and unaccounted for gas.

Why Does LAUF Matter?

If natural gas is burned, it becomes carbon dioxide, a greenhouse gas.  However, if it is leaked into the atmosphere before being burned, it is released as methane, a greenhouse gas that is 86 times more damaging to the climate. The potency of methane is why the 27,000+ gas leaks in Massachusetts hurts the climate roughly the same amount as the emissions of all of the state’s stores and businesses combined. (HEET SEI Report, pg. 5)

Some of these leaks are worse than others. Half of these emissions come from only 7% of the leaks, which are referred to as G3SEI (Grade 3 Significant Environmental Impact) leaks (Hendricks et. al. 2016). Utilities now have to repair these leaks, with HEET verifying the work as part of our shared action plan.

To reduce emissions we need to be able to measure our progress, so it’s important for utilities to provide standardized and accurate emissions estimates to the public and regulators. LAUF is how the utilities do this.

Components of LAUF Reporting

Columbia Gas’ LAUF itemization, 2019

The total amount of LAUF is calculated by subtracting the amount of gas the utility used and sold from the amount of gas they purchased. The utilities’ LAUF reports contain measurements or estimates of the following:

Lost gas

  • Fugitive emissions: Emissions from gas leaks
  • External damage: Emissions from damage to pipes by third parties 
  • Intentional venting and purging: Intentional release of gas for pipeline maintenance

Unaccounted for gas

  • Theft
  • Meter error
  • Billing cycle adjustment

This unaccounted for gas is not emitted into the atmosphere, but just not accounted for on the books.


The above amounts of gas are subtracted from the total amount of LAUF, and the amount that remains is labeled as unknown.

HEET worked hard in the Dept. of Public Utilities Technical Sessions on LAUF to create standard methods across the utilities that ensure data transparency and measurement. To this end we insisted that lost gas which could not be directly measured, estimated or identified as lost from a particular source should be designated ‘Unknown’. We hope that showing transparently the scale of what is not yet known will stimulate the inquiry and research needed to solve this ‘MA Methane Mystery’.

How are the fugitive emissions in LAUF calculated?

In 2019, the method for estimating annual fugitive emissions from leaks was suggested by HEET and agreed upon in discussions between regulators, utilities, and other non-profits including HEET. It takes as input the following:

  • Leak counts: The number of repaired and unrepaired leaks, and how many of each were G3SEIs (“super-emitting leaks”).
  • Average leak duration: The average amount of time that leaks had been open during the reporting year, for repaired and unrepaired leaks respectively.
  • Breakdown of leak repairs: The percentage of leak repairs that occured on each type of pipe material (cast iron, protected steel, unprotected steel, plastic), for mains and service lines respectively.

The calculation’s only other source of data is from research on average leak rates, also known as “emissions factors” (Lamb et al. 2015). These factors estimate how much gas is released from different types of leaks per minute, depending on the pipe material, whether it is a main or service line, and whether the leak is a G3SEI.

The information is then used to estimate emissions for each type of leak. The calculation is a sum of linear multiplications. An emissions estimate is made for each type of leak, and then the estimates are all added together to get the total. For example, here’s the calculation to estimate the emissions for National Grid from repaired cast iron G3SEI leaks:

(average length of time National Grid took to repair leaks that year)
x (number of repaired G3SEI leaks in National Grid territory)
x (percentage of cast iron pipe in National Grid territory)
x (“emissions factor” for cast iron G3SEI leaks)

To get the total emissions we’d then repeat this process for every combination of pipe material, G3SEI status, and repair status. The sum of these 16 estimates would be the total.

This method and data likely produce underestimates. It only takes into account leaks reported by the utilities, but independent researchers typically find 1.5 to 3 times as many leaks. Methane could also be leaking from pipes at a different rate than we assumed for this calculation. However, it’s still the best we can do with the available data, and many can agree it is a reasonable estimate for the minimum being leaked.

The LAUF calculator on this page replicates this same method.

Using the gas leaks emissions calculator

Please let us know if you have any questions or feedback about this! We’re here to help and always trying to improve this tool.

The LAUF calculator shows each utility’s inputs to the calculation and their calculated emissions. You can make changes to their numbers to see how the emissions estimate would change.

To use the calculator to estimate your town’s leak emissions, first select your town’s gas utility from the utility menu, and then replace the utility’s leak counts with your town’s leak counts. For example, to calculate Salem’s estimated leak emissions, select National Grid from the utility menu, and then update the total leak counts with the number of leaks reported in Salem. (Leak counts by towns can be found on the HEET gas leaks maps page.)

If you don’t know the exact number of G3SEIs in your town, then you can assume 7% of the leaks are G3SEIs and 93% of leaks are not G3SEIs. Any data you don’t change, will remain the same as reported by the utility. For example, if you only change the leak counts, then leak durations and repair breakdowns will stay the same as National Grid’s averages.

The calculator will then calculate an emissions estimate (in metric tons of carbon dioxide) from leaks in the municipality. This is an underestimate for the reasons stated above.

Be sure to check the following when entering data into the calculator to ensure a correct estimate:

  • All data should include leaks of all grades, not just grade 3 leaks. (There are also grade 1 and 2 leaks, which are considered the leaks that are more likely to be potentially explosive). 
  • If you’re calculating your town’s average leak durations:
    • The leak duration is the average number of days that it took for a leak to be repaired this year.  Therefore, no duration can be more than 365 days. The average leak duration should only be within the year the estimate is calculated for. All leak start dates used in the average should be truncated to January 1 if they began before then.
    • A single leak’s duration = (1 + end date – start date) / 365. A leak with the same reported repair date and start date should be considered to be open for 1 day, not 0.
  • If you’re calculating your town’s leak counts or durations, then “repaired” leaks refer to leaks repaired during the year you’re estimating emissions for.

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If you have questions, contact us!