How to read and look up an API well number

What the API number is

Most oil and gas wells in the United States carry an identifier called the API number, named for the American Petroleum Institute. API published the numbering scheme in Bulletin D12A, and the last edition came out in 1979. The scheme now lives on as the US Well Number, a standard maintained by the Professional Petroleum Data Management (PPDM) Association. That standard keeps the old numbers and states that a well's number should be permanent and never reused for another well.

You'll find the number on drilling permits, completion reports, plugging records, production reports, lease paperwork and royalty statements. Well names change when wells are sold or renamed, but the number stays the same, so it's the most reliable way to match a well across different documents.

The agency that issues the number is the state regulator, which the PPDM standard calls the "Primary Assigning Authority". PPDM maintains the format but doesn't issue numbers itself. Regulators usually assign the number when they receive the drilling permit application or approve the permit.

What each group of digits means

The number is often written with dashes, for example 47-087-03281. Here is what the digits mean:

1. Digits 1-2: state code. For example, 04 is California, 15 is Kansas, 17 is Louisiana, 35 is Oklahoma, 37 is Pennsylvania, 42 is Texas and 47 is West Virginia. These codes date back to a 1952 IBM list. They are not the FIPS codes the Census Bureau uses, so don't swap one for the other. Federal offshore waters have their own codes, such as 60 for the northern Gulf of Mexico.
2. Digits 3-5: county code. This is a county, a parish in Louisiana or a USGS quadrangle in Alaska. Each county code is unique only within its state. It doesn't match the FIPS county code either.
3. Digits 6-10: unique well code. This is a sequence number within the county. The number has no meaning about drilling order or date, and some states use number ranges for their own record-keeping. The first 10 digits together identify the well's surface location, the hole in the ground.
4. Digits 11-12: wellbore code. This identifies the original hole, a sidetrack or a new lateral drilled from the same surface location. Every wellbore drilled from one surface location shares the same first 10 digits.
5. Digits 13-14: extension. Some states add 2 more digits for events such as a recompletion or plugback. The standard doesn't define these digits, and states use them in different ways.

For example, 4708703281 starts with 47 (West Virginia) and 087 (the county code for Roane County). On WellCensus it is the Stockley, O. D. 54 well in Roane County.

Why you see 10, 12 and 14-digit versions

The PPDM standard itself notes that the old API number is applied inconsistently. It can be 10, 12 or 14 digits long, many regulators assign only 10 digits, and digits 11-14 mean different things in different places. A few regulators even assign the county code based on where a deviated well produces instead of where it starts at the surface.

In practice, this is how to handle the different lengths:

• Use the first 10 digits to identify the well. Every version of the number shares them.
• Remove dashes and spaces before you search. 42-123-45678, 4212345678 and 42123456780000 all start with the same 10 digits.
• Keep the leading zero. California's numbers start with 04 and Alabama's with 01. Spreadsheets often drop the zero, which leaves a 9-digit number that matches nothing.
• If you have a 12 or 14-digit number and a search returns nothing, try only the first 10 digits.

How to look a well up by its number

1. Read the first 2 digits to find the state. That state's oil and gas regulator holds the official record, including the permit, completion report and plugging report.
2. Search the 10-digit number on WellCensus. The search page recognizes an API number and takes you straight to that well. Its page shows the operator of record, status, well type, available dates, depth, county and location.
3. For scanned documents such as logs, inspection reports and production volumes, go to the regulator's own system. In Texas, for example, the Railroad Commission's public GIS viewer has an API search tool.
4. If the number doesn't turn up anywhere, check that the state code is right and that a leading zero wasn't dropped. Also check whether the record is very old. Wells drilled before API numbering may carry only a state record number. Indiana's registry, for instance, identifies wells by Indiana Geological Survey record IDs instead of API numbers.

What the record can and cannot tell you

A well record covers what the regulator tracks: who operates the well, whether it is producing, shut in, plugged or orphaned, when it was drilled and plugged, how deep it is and where it sits. It doesn't say who owns the minerals, who receives royalties or whether a lease is still in force. Those questions are answered by county deed and lease records and, where needed, by an attorney.

Coverage also varies by state. WellCensus carries 23 state registries. For two of them, Texas and Nebraska, the state's free bulk file is a location index. In those states a well's number, location and status class are listed, but the operator and dates may be missing. The methodology page lists what each state publishes.