Every barrel of crude that leaves a lease tank by truck is documented on a run ticket, and at the heart of that ticket are two numbers taken before and after the haul: the opening gauge and the closing gauge. The difference between them, once corrected, is how many barrels moved and how much the producer gets paid for. This guide explains how a tank run is measured from opening gauge through closing gauge, how gross volume becomes net barrels, why those gauge readings are the audit backbone of the ticket, and how automatic gauging and LACT data do the same job digitally.
Opening & Closing Gauge in one line: The opening gauge is the measured liquid level in a tank before a haul begins, and the closing gauge is the level after it ends. The difference between them gives the gross volume removed, which is then corrected for temperature and for sediment and water to arrive at net barrels. Recorded on the run ticket along with temperature and quality, the opening and closing gauge are the documented basis for how much oil was transferred and paid for.
A run ticket records a single transfer of crude out of a lease tank, and the measurement bookends it. Before any oil moves, the gauger establishes the opening gauge - the height of liquid in the tank, read against a calibrated tank table that converts the level to a volume. At the same time the gauger records the temperature of the oil and takes a sample to determine the basic sediment and water content, because both affect how the raw level translates into salable barrels. These opening figures capture the exact state of the tank at the instant the haul begins.
After the truck has loaded and the transfer is complete, the gauger takes the closing gauge - the new, lower liquid level - and the difference between opening and closing, read through the tank table, gives the gross observed volume that left the tank. Whether the reading is taken by hand with a gauge line and bob or by an automatic tank gauge, the principle is the same: two levels, before and after, define the volume moved. The run ticket ties these readings together with the date, time, tank identification, temperature, and quality, producing a complete, self-contained record of one haul that both the producer and the purchaser can rely on.
The gross observed volume that the opening-to-closing difference produces is not yet the number anyone gets paid on, because it reflects the oil as it sat in the tank rather than on a standardized basis. Two corrections turn gross into net. First, temperature: liquids expand when warm and contract when cool, so the volume is corrected to a standard reference temperature, ensuring a barrel means the same thing regardless of how hot the oil was in the tank. Without this correction, the same oil would appear to be a different quantity on a hot afternoon than on a cold morning.
Second, quality: crude coming off a lease carries some water and sediment that are not salable oil, and the basic sediment and water measurement taken during gauging quantifies that fraction. Removing it leaves only the merchantable oil. Applying the temperature correction and subtracting the sediment and water yields the net barrels - the standardized, quality-adjusted volume that the settlement is actually built on. The chain is therefore opening gauge and closing gauge give gross volume, temperature correction and sediment-and-water deduction give net barrels, and net barrels drive the payment. Each step has to be documented on the ticket so the path from raw level to paid volume is fully traceable.
Because the gauge readings are the foundation of the entire ticket, they are also its most vulnerable point when taken by hand. A manual gauge depends on a person reading a level correctly, recording it accurately, and sampling representatively, and honest human error - or worse, a dispute over what a reading actually was - can put real money in question. The opening and closing gauge are the audit backbone of the run ticket precisely because everything downstream inherits any error in them, which is why the industry has moved toward removing the hand from the measurement wherever the volume justifies it.
Automatic tank gauging and lease automatic custody transfer, or LACT, units are the digital equivalent of the opening-to-closing hand gauge. An automatic tank gauge continuously measures level, temperature, and often water content, so the opening and closing states are captured electronically rather than by a person climbing the tank. A LACT unit meters oil as it transfers and applies the temperature and quality corrections automatically, producing net barrels directly. A cloud SCADA platform such as Merobix carries that automatic gauging and LACT data into a timestamped record, so the levels, temperatures, and volumes that a paper run ticket once captured by hand are logged continuously and available to both parties. The result is the same audit trail the run ticket always provided - opening state, closing state, and the corrected volume between them - but produced without hand-gauge error and without the disputes that two people reading a tape can create.
The opening gauge is the tank's liquid level measured before a haul begins, and the closing gauge is the level after it ends. Read against a calibrated tank table, the difference between them gives the gross volume of oil that left the tank during the transfer. Both are recorded on the run ticket along with temperature and quality so the amount moved is fully documented.
The opening-to-closing difference gives gross observed volume, which is then corrected two ways. A temperature correction adjusts the volume to a standard reference temperature so a barrel means the same thing regardless of how warm the oil was, and the basic sediment and water fraction measured during gauging is subtracted to remove non-salable water and solids. What remains is net barrels - the standardized, quality-adjusted volume the payment is based on.
An automatic tank gauge continuously measures level, temperature, and often water content electronically, capturing the opening and closing states without a person reading a tape. A LACT unit meters oil as it transfers and applies temperature and quality corrections automatically to produce net barrels directly. Feeding that data into a SCADA record gives both parties the same opening-state, closing-state, and corrected-volume audit trail the run ticket always provided, but without hand-gauge error or reading disputes.
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