API Publication 300-1991: Principles and Practices for Petroleum Liquid Measurement

Scope and Overview

API Publication 300 (1991) is an industry reference document developed by the American Petroleum Institute to establish uniform guidelines for the measurement of liquid hydrocarbons during custody transfer operations. Although classified as a publication rather than a full standard, it provides foundational principles that have been widely adopted in terminals, refineries, and pipeline facilities. The document addresses the entire measurement chain, from tank gauging and meter proving to the computational methods required for accurate volume and mass determination.

The publication covers both static (tank) measurements and dynamic (meter) measurement systems. It emphasizes the use of standardized correction factors for temperature, pressure, and API gravity, and offers practical examples for calculating net standard volumes. While API Publ 300-1991 is not a replacement for the more comprehensive API Manual of Petroleum Measurement Standards (MPMS), it serves as a concise field reference for technicians and engineers who require quick access to essential measurement formulas and tables.

Technical Requirements and Calculation Methods

Temperature and Gravity Corrections

API Publ 300 details methods for correcting observed liquid volumes to standard conditions (60 °F and 0 psig). The key parameters include:

• API Gravity – base density referenced to 60 °F.
• Observed Temperature – measured in the tank or pipeline with calibrated thermometers or RTDs.
• Volume Correction Factor (VCF) – derived from API MPMS Chapter 12.2 tables or the corresponding ASTM D1250 tables.
• Pressure Correction Factor – applies to liquids under high pressure (typically >100 psig).

Table of Common Measurement Parameters

Calculation Workflow

The recommended workflow involves three sequential steps:

1. Observed Volume Measurement – from tank strapping tables or meter pulses.
2. Temperature and Gravity Sampling – at representative locations and times.
3. Correction to Standard Conditions using VCF and, if required, C_pl.

Implementation and Industry Application

Although API Publ 300-1991 is not a mandatory regulation, it has been integrated into many company operating procedures and custody transfer agreements. Facilities implementing its recommendations typically see improvements in measurement repeatability and a reduction in disputes over volume differences.

Key implementation considerations include:

• Equipment Calibration – temperature sensors and flow meters should be verified against national standards (NIST-traceable).
• Training – field operators must understand the concept of base volume and how to use the correction tables correctly.
• Documentation – all measurements, corrections, and intermediate results should be recorded in a format that allows third-party audit.

Compliance and Quality Assurance

Compliance with API Publ 300 is typically achieved through:

• Internal Audits – comparing field procedures against the publication’s recommendations.
• Proving and Verification – regular meter proving using master meters or gravimetric methods, with results recorded and trended.
• Document Control – ensuring that the 1991 edition is either still in use or that a documented transition to a newer MPMS chapter is in place.

For operations that are subject to regulatory oversight (e.g., pipeline tariffs, customs, or tax authorities), API Publ 300 can be used as a reference to demonstrate due diligence in measurement practices. However, regulators may require compliance with more current standards such as API MPMS Chapter 12.2 (2014) or a specific jurisdiction’s prescribed method.

Frequently Asked Questions

This article is for informational purposes and reflects the state of API Publ 300-1991 as of 2026. Users should verify current editions with the American Petroleum Institute.