Dictionary:API well number
A unique number assigned by the American Petroleum Institute to each well drilled in the United States. A 12-digit decimal number which is broken down as follows: Digits 1, 2: Code for state; numbers 1 to 49 are alphabetical for the states including the District of Columbia; Alaska and Hawaii are 50 and 51, 60 for Federal waters. Digits 3–5: Code for county, parish, or offshore. Digits 6–10: Code for the specific well. Digits 11–12: Code for sidetrack. 13–14: recompletion; etc. See API Bulletins D12 and D12A.