API Well Number Lookup: What It Is and How to Read One

An API well number is the unique identification code assigned to every oil and gas well drilled in the United States [1]. It runs from 10 to 14 digits, and no two wells anywhere in the country share the same one [1]. To look one up, read the leading digits for the state and county, then query the well in a state database or a multi-state map [2]. Operators and regulators lean on that number to tie a well’s permit to its later production and emissions filings [2]. On TetraSoft Atlas, a subscription platform for oil and gas records, every well shows its API-10 number beside the operator and its production history [3].

Quick Answer: An API well number is a unique 10 to 14 digit code for a single oil and gas well [1]. Read the first digits for the state and county, then look the well up in a state database or on TetraSoft Atlas [2].

Atlas maps more than 2.5 million wells across eight states, each one clickable to its full record.

What Is an API Well Number?

An API well number is a permanent ID that a state agency assigns to a well when it issues the drilling permit [2]. Its core is ten digits in fixed blocks: two for the state, three for the county, and five for the individual well [1]. Those first ten digits are the API-10, the form most databases store and display [1].

Up to four more digits can follow, for a full API-14, but only when a well needs them [1]. A simple single-bore well stops at ten, while wells with sidetracks or extra completions carry the 12- or 14-digit forms [1].

State codes run in alphabetical order, from 01 for Alabama to 49 for Wyoming, then 50 for Alaska and 51 for Hawaii [1]. The American Petroleum Institute standardized the scheme in its D12A bulletin [1]. The full set of codes fits in one compact table.

Code	State	Code	State	Code	State
01	Alabama	18	Maine	35	Oklahoma
02	Arizona	19	Maryland	36	Oregon
03	Arkansas	20	Massachusetts	37	Pennsylvania
04	California	21	Michigan	38	Rhode Island
05	Colorado	22	Minnesota	39	South Carolina
06	Connecticut	23	Mississippi	40	South Dakota
07	Delaware	24	Missouri	41	Tennessee
08	District of Columbia	25	Montana	42	Texas
09	Florida	26	Nebraska	43	Utah
10	Georgia	27	Nevada	44	Vermont
11	Idaho	28	New Hampshire	45	Virginia
12	Illinois	29	New Jersey	46	Washington
13	Indiana	30	New Mexico	47	West Virginia
14	Iowa	31	New York	48	Wisconsin
15	Kansas	32	North Carolina	49	Wyoming
16	Kentucky	33	North Dakota	50	Alaska
17	Louisiana	34	Ohio	51	Hawaii

The county digits pin the well to one county, fixed from its surface location rather than the bottom of the bore [1]. A horizontal well that runs across a county line keeps the code of the county where it starts [1]. Its bottomhole can sit elsewhere, yet the API number holds [1]. Operators new to the format often expect the number to follow the producing formation, not the wellhead.

How do you read the digits of an API number?

You read an API number left to right, from the widest location down to the single well [1]. Take the Oklahoma well 3513722789 [3]. The 35 marks Oklahoma, the next three digits point to Stephens County, and the final five identify that one well [2].

The last four digits handle wells that are not simple single bores [1]. The first extra pair marks a sidetrack drilled off the original hole; the second pair records a later recompletion [1]. Take that same well 3513722789: a first sidetrack makes the 12-digit form 351372278901, where the 01 identifies the sidetrack [1]. A recompletion appends one more pair, so the 14-digit form reads 35137227890101 [1].

How Do You Look Up a Well by Its API Number?

You look up an API well number in the state agency database that issued it, matched by the state code [2]. Each state runs its own well system keyed to those numbers [2]. Texas wells sit in the Railroad Commission of Texas records, and Colorado wells sit in the Energy and Carbon Management Commission (ECMC) database [2]. New Mexico, Oklahoma, Ohio, Pennsylvania, West Virginia, and Wyoming each run an equivalent agency system [2].

The search itself takes one field. Enter the API number in the agency’s well search, and the record returns the operator, location, status, and permit history [2]. Because the number never changes, it stays valid even after a well changes hands [2].

Which agency database matches each state code?

Match the leading two digits to the agency that runs that state’s wells [2]. Code 05 routes to Colorado’s ECMC, and 35 routes to the Oklahoma Corporation Commission (OCC) [2]. Each agency runs a public well search that accepts the API number [2].

State portals format the number in different ways [2]. Some take the full 10 digits with or without dashes, and Texas records often drop the 42 state prefix [2]. Keep the full API-10 on hand, and you can match a well in any state system.

The same number reaches past the permit record, threading through production and enforcement filings held in separate systems [2]. For a worked state example of those records cross-linked, see our COGCC (Now ECMC) Oil & Gas Data, Cross-Linked and Faster Than the State Portal.

Where Can You See Wells and Their API Numbers Across States?

TetraSoft Atlas maps millions of wells across eight states and shows each well’s API-10 on its record [3]. The map covers Colorado, Texas, New Mexico, Oklahoma, Wyoming, West Virginia, Pennsylvania, and Ohio, and TetraSoft is actively adding more states over time [3]. Together those states hold more than 2.5 million wells, with Texas alone above 1.2 million. One search box covers them all.

You locate a well on the map, or by its name and operator, then open its record [3]. The panel leads with the API-10 number, next to the operator and the well’s status, with production and gas composition a tab away [3]. For a single-state view of the same idea, see our Colorado Oil & Gas Map: Emissions and Enforcement Data.

An Oklahoma well record in Atlas: the API-10 number leads, beside the operator and county. [3]

Frequently Asked Questions

How many digits is an API well number, and why does the length vary?

An API well number holds up to 14 digits, but the first 10 do the everyday work [1]. That API-10 already names one wellbore, which is why most databases display and search on it [1]. The length varies because the extra digits are optional, added only for wells with sidetracks or multiple completions [1].

Does an API well number ever change?

An API well number stays fixed for the life of the well [2]. A change in operator or ownership does not alter it [2]. That permanence lets the number act as the join key across separate agency systems [2].

Is an API number the same as a drilling permit number?

No, the two identifiers serve different roles [2]. A drilling permit number tracks the application to drill, and each state formats it differently [2]. The API number identifies the physical well and follows the national format in every state [1]. You use the API number, not the permit number, to match a well across agencies.

What does a state code above 49 mean?

Codes above 49 cover wells outside the original lower-48 numbering [1]. Alaska carries 50 and Hawaii carries 51, and higher numbers mark offshore federal waters [1]. The reading rule does not change, since the first two digits still name the jurisdiction [1].

Is the API well number being replaced by a US Well Number?

Not in practice yet [1]. The industry has proposed a longer US Well Number to fix format gaps and cover wells the old scheme cannot number [1]. State agencies still assign and publish the API number as the primary well identifier today. You look up wells by API number in every state system covered here [2].

A well’s records all trace back to one number, and Atlas puts wells from eight states on one map with that API-10 attached [3]. Start your free 7-day trial.

This post is for informational purposes only and does not constitute legal or compliance advice. Consult qualified legal counsel or a compliance professional for guidance specific to your operations and jurisdiction.

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References

1. American Petroleum Institute, Bulletin D12A well numbering standard (1968; 1979 revision), now maintained by the Professional Petroleum Data Management (PPDM) Association.
2. U.S. state oil and gas regulatory agency well databases (RRC Texas, ECMC Colorado, OCC Oklahoma, and peer state agencies).
3. TetraSoft Atlas, multi-state oil and gas dataset and product features. https://tetrasoftco.com/atlas-landing.html

Interactive tool

Decode an API well number

10, 12 and 14 digit forms all work. Nothing leaves your browser.

Try 42-329-33445 05-123-05462 14-digit

State codes follow the American Petroleum Institute D12A standard; county names come from US Census county FIPS codes, which the API county code uses.