State or pseudo-state — digits 1–2
Identifies the surface state or an offshore pseudo-state. It does not change when the bottom-hole location crosses into another state.
Sourced field guide · Updated July 28, 2026
How to read an API well number
Decode API-10, API-12 and API-14 identifiers, distinguish API state codes from FIPS codes, and understand what a missing lookup result can—and cannot—tell you.
Three common lengths
API-10 identifies the state/county/well core; API-12 adds a wellbore code; historical API-14 adds an event field.
Surface location rules
The state and county portions describe the surface location, even when a directional well crosses a boundary underground.
A lookup is not existence proof
A positive record can identify a well. An empty result only describes the database and coverage that were queried.
Start here
API Well Number vs. US Well Number
“API number” remains the language used in many leases, regulator portals and datasets. The standard itself has moved on.
The historical API Well Number was designed to give US wells and wellbores a consistent identifier. In 2010, the American Petroleum Institute transferred stewardship to the Professional Petroleum Data Management Association. PPDM's US Well Number Standard is the official successor.
The successor keeps continuity with historical API identifiers while more explicitly separating a well origin from its wellbores. This matters because one surface origin can lead to multiple laterals, sidetracks or other wellbores.
Do not assume every record has 14 digits. Historical data, regulator exports and vendor systems commonly expose API-10, API-12 or API-14. Modern US Well Number extensions are optional and are not safely interpreted as one universal two-digit completion counter.
Identifier anatomy
Decode the historical API-14 format
Use 42-161-00101-00-00 as a worked example. The colors below separate fields; the dashes are formatting, not additional data.
42
State
Digits 1–2
Texas
161
County
Digits 3–5
County code
00101
Well code
Digits 6–10
Unique well code
00
Wellbore
Digits 11–12
Original bore
00
Event
Digits 13–14
Original event
County or equivalent — digits 3–5
Identifies the surface county or offshore equivalent. Combined with the state code, it locates the jurisdictional origin.
Unique well code — digits 6–10
Usually unique within the county. Some regulator implementations base it on a permit number that is unique at state level, so do not infer chronology from the value.
Wellbore / sidetrack — digits 11–12
Historically identifies the original wellbore or a sidetrack. Older exports may omit it; the current US Well Number standard requires a wellbore code.
Historical event sequence — digits 13–14
Historically used for operations on a wellbore, such as a plugback or recompletion. Interpretation can differ by regulator or data vendor.
Formatting and leading zeroes
Dashes are optional display characters. Leading zeroes are not optional data: store identifiers as text, never as spreadsheet numbers.
Length guide
API-10, API-12 and API-14
The same well family can appear at different levels of specificity. Preserve what the source supplied before normalizing it.
42-161-00101
State + county + well code
Common in historical and regulator records. It does not identify a particular wellbore.
42-161-00101-00
API-10 + wellbore code
Adds the original or subsequent wellbore. Texas map data commonly exposes a 12-digit APINUM.
42-161-00101-00-00
API-12 + historical event sequence
The classic full format. Treat the last field as source-specific when combining datasets.
Reference table
Historical API state and offshore codes
These codes come from the historical API numbering system. They are intentionally different from postal and FIPS codes. Offshore entries are pseudo-states used by the identifier system.
01
Alabama
02
Arizona
03
Arkansas
04
California
05
Colorado
06
Connecticut
07
Delaware
08
District of Columbia
09
Florida
10
Georgia
11
Idaho
12
Illinois
13
Indiana
14
Iowa
15
Kansas
16
Kentucky
17
Louisiana
18
Maine
19
Maryland
20
Massachusetts
21
Michigan
22
Minnesota
23
Mississippi
24
Missouri
25
Montana
26
Nebraska
27
Nevada
28
New Hampshire
29
New Jersey
30
New Mexico
31
New York
32
North Carolina
33
North Dakota
34
Ohio
35
Oklahoma
36
Oregon
37
Pennsylvania
38
Rhode Island
39
South Carolina
40
South Dakota
41
Tennessee
42
Texas
43
Utah
44
Vermont
45
Virginia
46
Washington
47
West Virginia
48
Wisconsin
49
Wyoming
50
Alaska
51
Hawaii
55
Alaska Coast
Pseudo-state
56
Pacific Coast
Pseudo-state
60
Gulf of Mexico
Pseudo-state
61
Atlantic Coast
Pseudo-state
Source: New York State Museum API Number guide. Verify regulator-specific county codes against the regulator that issued the record.
Practical workflow
How to decode and verify a well number
A safe workflow preserves the source identifier, separates decoding from verification, and never turns unavailable data into a negative fact.
- 1
Keep the identifier as text
Preserve leading zeroes and remove only formatting characters such as spaces or dashes. Do not store a well number as a spreadsheet number.
- 2
Count the digits
Identify whether the source supplied API-10, API-12 or API-14. Do not infer omitted wellbore or event values unless your workflow explicitly normalizes them.
- 3
Decode the segments
Read the state or pseudo-state code, county code and well code. If present, read the wellbore and historical event-sequence fields.
- 4
Verify against the source record
Use a state regulator or a production-record lookup. Treat missing records as unavailable data, not proof that a well is nonexistent.
Interpret an empty result carefully
If OilPriceAPI returns no production record, that does not prove that the well does not exist. It may be permitted without production, outside current well-level coverage, or represented differently by the source regulator.
Supported product path
Retrieve available production records
OilPriceAPI's verified well lookup is backed by monthly production filings—not a fabricated permit record. The customer endpoint accepts a normalized 14-digit identifier.
Real worked example
42-161-00101-00-00
QUANICO OIL & GAS, INC. · Texas · monthly filings available in the verified lookup dataset.
Authenticated request
curl "https://api.oilpriceapi.com/v1/well-production/wells/42161001010000" \
-H "Authorization: Token YOUR_API_KEY"
{
"status": "success",
"data": {
"api_number": "42161001010000",
"operator": "QUANICO OIL & GAS, INC.",
"well_name": "WILSON, W. D. & WIFE",
"state": "TX",
"count": 397,
"data": [
{
"period": "1993-01",
"oil_bbl": 5,
"gas_mcf": 1,
"water_bbl": 0,
"days_producing": 31,
"source": "tx_rrc"
}
]
}
}The example shows the response shape and a real record. The array is abbreviated for readability; use returned periods and source fields rather than assuming current production.
Frequently asked questions
API well number FAQ
What is an API well number?
An API well number is the historical United States identifier created under the American Petroleum Institute numbering system. Its familiar 10-digit core identifies a state or pseudo-state, a county or equivalent area, and a well code. The PPDM US Well Number is the official successor to the API Well Number.
Are all API well numbers 14 digits?
No. Source systems commonly expose 10-digit API numbers, 12-digit numbers with a wellbore code, or the historical 14-digit form with an event-sequence suffix. Some historical records predate complete wellbore coding, and regulator implementations vary.
What does 42 mean at the start of an API number?
In the historical API state-code list, 42 means Texas. It is an API numbering-system code, not the Texas FIPS state code. The first five digits are based on the well's surface state and county, even when the bottom-hole location crosses a boundary.
What are the last four digits of an API-14 number?
Under the historical format, digits 11 and 12 identify the wellbore or directional sidetrack, while digits 13 and 14 are the event-sequence code used for operations such as a recompletion or plugback. Vendors and regulators may implement the final field differently.
Is the API Well Number still the current standard?
The name remains common in regulatory and commercial datasets, but PPDM's US Well Number is the official successor. API transferred stewardship of the standard to PPDM in 2010. The successor standard retains continuity with the historical identifier while better distinguishing well origins and wellbores.
Does no OilPriceAPI result mean the well does not exist?
No. The lookup checks production records available to OilPriceAPI. No result means the service holds no matching monthly production record; it does not prove that the well does not exist. A well may be permitted but never have reported production, or its state may not be covered at well level.
Method and provenance
Authoritative references
Identifier standards are easy to misstate because legacy API, current US Well Number and regulator-specific exports coexist. This guide uses standards and regulator sources.
PPDM US Well Number Standard
Current stewardship, successor-standard status and well-identification framework.
New York State Museum API Number Guide
Historical segment definitions, examples, surface-location rule and API state-code list.
NYSDEC Well Database Help
Regulator field definitions for the 14-digit identifier, sidetrack and completion fields.
BOEM Well Field Definitions
Federal offshore definition of state/area, county/area, unique well and sidetrack fields.
Railroad Commission of Texas
Texas regulator documentation confirming Texas code 42 and 10/12-digit map-data variants.
Start with a real production-record lookup
Paste an API-10, API-12 or API-14 identifier. OilPriceAPI normalizes the input and returns verified production data when a matching record is available.