Lease Automatic Custody Transfer (LACT) systems sit at the hand-off point in oil and gas: the exact moment barrels change owners and dollars change hands. 

A LACT skid automates that exchange: measuring, sampling, and documenting flow so producers, pipelines, and refiners all trust the numbers. In modern operations, these packages replace error-prone manual tasks with repeatable, auditable routines that run 24/7.

It’s not just bookkeeping. Accurate custody transfer affects royalties, revenue splits, nominations, and downstream planning. 

Federal rules tie these transactions to specific accuracy, proving, and recordkeeping requirements. Notably the Bureau of Land Management’s oil-measurement regulations for federal and Indian leases. So, the data must be both correct and defensible.

At its core, custody transfer measurement aims for three things: accuracy, repeatability, and traceability. The system needs to quantify how much product moved, at what conditions, and with what quality. Then prove those results can be reproduced and audited later.

That’s why LACT systems don’t rely on a single device. They combine primary measurement (flow meter), condition measurements (temperature and pressure), sampling/quality checks, and a flow computer that applies recognized correction factors and builds the “paper trail.”

When temperature, pressure, composition, viscosity, or flow profile shift, the system corrects to standard conditions following API MPMS methods and preserves the evidence as part of an audit trail.

Technology choice is application-specific.

• Coriolis meters directly measure mass flow and density for high-accuracy liquid measurement.
• Turbine and positive-displacement meters provide excellent volumetric performance when sized and installed correctly.

The “right” answer depends on fluid, rangeability, operating envelope, and your target uncertainty.

Primary meter. The heart of the skid. Coriolis, PD, and turbine meters are common in custody transfer liquids. Selection hinges on viscosity, solids content, flow range, and required uncertainty.

Temperature & pressure. These are not afterthoughts: volume correction to base conditions lives and dies on temperature and pressure accuracy. Good practice includes redundant sensors and strict calibration intervals.

Sampling/quality. Representative samples (composite or continuous) feed density/BS&W labs or online analyzers, reducing disputes over quality adjustments.

Flow computer & data. The flow computer applies API correction factors, stores results with time-stamped audit trails, and produces custody transfer tickets. This is your “single source of truth” in an inspection.

For fiscal/custody transfer of liquid hydrocarbons, industry guidance typically targets overall measurement uncertainty on the order of ±0.25% or better. 

That threshold reflects the financial stakes and the expectation that parties can reconcile volumes without material bias. 

Hitting that mark requires the whole chain to perform within spec, not just the primary meter. The chain includes meter, installation, proving, temperature/pressure inputs, sampling, and data handling.

Errors in temperature or pressure feed directly into wrong base-volume calculations; poor installation (piping effects, entrained gas, pulsation) can bias a meter; and drifting instruments quietly erode accuracy over time. Routine calibration and rigorous proving are how you keep the whole stack honest.

The American Petroleum Institute’s Manual of Petroleum Measurement Standards (API MPMS) is the shared language of custody transfer. It standardizes how equipment is specified and installed, how meters are proved and factors are calculated, and how results are documented and audited.

Using MPMS methods keeps you interoperable across operators and jurisdictions. Giving you a defensible basis when regulators or counterparties review your numbers.

Three chapters matter constantly in LACT work:

• MPMS Ch. 6.1/6.4A (Lease Automatic Custody Transfer) cover design, installation, operation, and maintenance practices for LACT systems, including meter selection, proving, and data handling.

• MPMS Ch. 18.2 addresses custody transfer principles and procedures, including uncertainty evaluation and documentation expectations for “defensible” measurement.

• MPMS Ch. 13.2 provides the statistical toolbox for analyzing proving data, calculating meter factors, and evaluating uncertainty. Critical for turning multiple runs into a valid factor with confidence bounds.

On federal and Indian leases, the BLM’s oil-measurement rules in 43 CFR Part 3174 define required performance (accuracy), proving, sealing, and recordkeeping. Explicitly anchor compliance to recognized standards like API MPMS.

If you operate LACT sites in this space, your procedures, calibrations, and data retention must map cleanly to these rules. Many states layer on additional requirements, so your compliance matrix should reconcile both federal and state expectations.

Proving compares the meter’s indicated volume to a reference standard under controlled conditions to derive a meter factor. 

Proving is not optional for custody transfer. It’s the way you demonstrate traceability to national standards and keep bias out of your tickets. Frequency is defined by your standard/regulator and by operating conditions. 

Historically, the BLM’s Onshore Order 4 framework pointed to quarterly proving, and later rulemakings updated the structure under Part 3174. The takeaway: set your intervals by rule and risk, and stick to them.

Prover Options and When to Use Them

• Bidirectional pipe provers run multiple passes without returning the displacer to the start, boosting efficiency while maintaining high accuracy. They’re the gold standard for liquid custody transfer where space and budget allow.

• Unidirectional pipe provers return the displacer between runs; the simpler flow pattern can offer excellent repeatability. Choice often hinges on layout and operations.

• Compact provers reduce footprint and can meet custody goals where space is limited; useful on retrofits or constrained sites.

• Master meter provers reference a well-characterized “master” that’s itself maintained to primary standards. Uncertainty is higher than pipe proving, so ensure the total measurement uncertainty still meets contractual/regulatory limits.

Running a Prove That Stands Up to Audit

1. Stabilize conditions. Temperature, pressure, and flow should be steady; confirm prover readiness and displacer integrity.

2. Execute multiple runs. Follow your procedure to capture enough valid passes for statistical confidence; investigate outliers before excluding them.

3. Apply MPMS 13.2 statistics. Calculate the factor, standard deviation, and confidence intervals; document any trend or bias you discover and the corrective action taken.

4. Close the loop. Load the new factor, seal as required, and archive the complete packet: pre-checks, raw runs, calculations, certificates, and signoffs.

A reliable LACT starts on the drawing board:

• Engineer for measurement, not just mechanics. Provide straight-run and flow conditioning as needed; mitigate entrained gas and pulsation; size meters for their sweet spot; and select temperature/pressure instruments with the accuracy that your uncertainty budget requires.

• Plan for proving and maintenance. Give yourself prover connections, safe access, and isolation points. Make calibration and sampling physically easy so technicians actually do them—and do them right.

• Harden the environment. Protect instruments from vibration, electrical noise, temperature extremes, and corrosion; these are the quiet killers of measurement integrity.

Commissioning then proves that the build matches the intent: loop checks, calibrations, alarm logic, proving, and full document verification before hydrocarbon custody goes live.

SOPs should spell out startup/shutdown, routine monitoring, alarm response, sampling, calibration intervals, and proving cadence—with clear acceptance limits. Operators need to know not only what to do, but what good looks like.

Training blends classroom fundamentals (API methods, uncertainty, custody mechanics) with hands-on proving and ticketing practice. Refresher cycles keep skills current and guard against drift.

Preventive maintenance covers meters, transmitters, analyzers/samplers, flow computers, seals, and security. A small drift in a temperature element can undo an otherwise perfect prove.

Quality control means in-situ diagnostics, alarm management, and periodic data reviews. Trend meter factor, temperature/pressure deltas, sampling representativeness, and ticket variance. Catch change early; confirm with a targeted prove.

• Meter factor creep that no one notices until reconciliation blows up—solve with trend reviews and timely re-proving. 
• Bad temperature/pressure causing wrong base volumes—use high-grade sensors, verify routinely, and keep redundancy. 
• Sampling that isn’t representative—fix grab-point design, agitation, and timing; validate with lab feedback. 

Data integrity gaps—treat the flow computer as a regulated device: manage security, time sync, firmware control, and audit trails that satisfy API and BLM reviewers.

If you remember one thing, make it this: custody transfer performance is systemic. You don’t “buy accuracy”—you build it with design, proving, disciplined operations, and documentation that maps to API MPMS and your regulator’s rulebook.

A good starting checklist:

• Map your uncertainty budget (can you really meet ±0.25% with the current stack?).

• Align every procedure with API MPMS chapters you can cite on request (6.x for LACT, 13.2 for stats, 4.x for proving hardware, 18.2 for custody principles).

• Validate that your proving program meets your jurisdiction’s expectations (e.g., legacy Order 4’s quarterly cadence and the current Part 3174 structure).

• Close the loop with clear SOPs, training, and routine QC—including trend reviews that trigger action before small errors become big disputes.

The payoff: smoother tickets, fewer partner disputes, cleaner audits, and higher confidence across your value chain.