API Numbers Explained

Contact: Office of Oil, Gas, and Minerals

You may notice that Michigan’s use of the American Petroleum Institute (API) numbering system (the API number) for new oil and gas permits has changed.  The change affects the 6th through 10th digits of the 14-digit API number and was initiated the week of March 6, 2017, which coincides with Michigan’s implementation of a new oil and gas database (RBDMS.NET)

The API numbering system is a standard that creates a unique and permanent number used to identify oil and gas wells throughout the country. Michigan not only applies this system to Part 615 oil and gas wells, but also to Part 625 mineral wells.  The API number consists of five parts:

  1. The first two digits represent the state code. ‘21’ is the state code for Michigan.
  2. The next three digits represent the county code which is determined by the county where the well’s surface is located. County codes in Michigan start with ‘001’ for Alcona County, increasing by two for each county until the last county, Wexford County ‘165’ - is reached.
  3. The next five digits are a unique well identifier for that particular county and this represents the change that we have implemented. In the past, Michigan populated this part of the API number (6th through 10th digits) with the well’s five digit permit number. Until 1998, Michigan did not use API numbers and the five digit permit number was a well’s only identification. To be consistent with other states, the 6th through 10th digit part of the API number is no longer tied to the five digit permit number. To highlight the change from the previously used API numbering scheme, we have jumped forward to ‘62000’ in this part of the API number, and will add to that number (i.e. ‘62001’, ‘62002, ‘62003’ and so on) based upon the next well permitted in that particular county. This change will only impact permits issued after 3/6/2017, so any previously issued API numbers will remain the same. As a result of this change, there will be duplication in the 6th – 10th digit part of API number for different wells, but the entire API number will remain unique for a given well because of the county code. 
  4. The next two digits are used to represent kicks or re-drills from the initial well bore. Some examples include: horizontal re-drills, directional re-drills, deepenings, and re-entries of plugged wells. For the initial well, the API number is designated by a ‘00’ in the 11th and 12th digits of the API number and any subsequent re-drills  are designated by ‘01’, ‘02’, ‘03’, and so on. It should be pointed out that there are also special cases - unique to Michigan - where the 11th and 12th digits are ‘70’ for mineral wells, ‘80’ for some brine disposal wells, and ‘90’ for wells drilled before permits were issued (pre-1927).
  5. The last two digits are used in Michigan to document lost holes and designated with a ‘90’ in the 13th and 14th digits of the API number. Michigan also uses the 13th and 14th digits when a blanket mineral well permit is issued for more than a single test hole.  The individual holes for the blanket permit are designated by ‘01’, ‘02’ and so forth in the 13th and 14th digits.

Should there be any questions about API numbering and Michigan’s changes, please do not hesitate to contact Mark Snow, DEQ-Oil, Gas, and Minerals Division, Supervisor, Permits and Bonding Unit, at snowm@michigan.gov; or 517-230-8233.