API Well Number

The API well number is the universal identifier for oil and gas wells in the United States. Every well drilled since the system was adopted carries a unique API number that follows it through its entire regulatory and production life. It is the primary key that links permit records, wellbore data, production history, completion records, and ownership information across different state and federal databases.

Structure of the API Number

A full API number contains 14 digits organized into four components:

42  - 101  - 12345  - 00  - 00
↑     ↑       ↑       ↑     ↑
State County  Unique  Sidetrack Perforation
Code  Code    Well ID  Code    Code

• State Code (2 digits): Texas = 42, New Mexico = 30, Colorado = 05, North Dakota = 33
• County Code (3 digits): FIPS county code within the state
• Unique Well ID (5 digits): Sequential number assigned by the state regulatory agency
• Sidetrack Code (2 digits): 00 for the original wellbore; increments for each sidetrack
• Perforation Code (2 digits): Identifies specific completion intervals

API-10 vs. API-12 vs. API-14

Different databases use abbreviated forms. API-10 drops the sidetrack and perforation codes. API-12 drops only the perforation code. When joining data across sources, it is critical to standardize to the same length — a mismatch between API-10 and API-14 formats is one of the most common causes of failed data joins in O&G analytics pipelines.

Why It Matters for Data Users

The API number is how EnergyNetWatch links production records from the Texas RRC to permit records, completion data, and geographic coordinates. A well's API number does not change when it changes operators, is reworked, or is transferred — making it the only reliable cross-source identifier.