An API number is a unique and permanent number that identifies each well drilled for oil and gas in the United States. API numbers were established by the American Petroleum Institute, as an industry standard, to keep track of the nearly three million oil and gas drills in the country. It was necessary because wells usually have names that consist of three parts: an operator name, a well number and a lease name. All three parts are subject to change, so there had to be a way to track them as they were sold and leased to different companies.
Example of an API Number
Locate the API number somewhere on the base of the oil or gas well. This number is usually clear and easy to find. The paperwork associated with each well describes the exact location. Each API number has up to 14 digits, divided by dashes. The example used by the Society of Petrophysicists and Well Log Analysts (SPWLA) is "42-501-20130-03-00."
Look for the first set of digits in the API number, which is the state code. In the above example, "42" is Texas. All state codes, which are listed on the SPWLA website, are based on standard codes proposed by IBM in 1952 for accounting purposes. The states are numbered from 01 (Alabama) to 49 (Wyoming); the District of Columbia is 08. This scheme was developed before Alaska and Hawaii joined the United States, so their numbers, respectively, are 50 and 51. Numbers 52 to 54 are reserved for future states like Puerto Rico, and numbers 55 to 61 are reserved for "pseudo-states," or for offshore federal waters that have oil wells.
Check the second group of digits in the API number, which is the "county code." In the above example, "501" is Yoakum County, in the northwest part of Texas along the New Mexico border. County codes are usually odd numbers to allow for expansion of the database of wells.
Take note of the third group of digits in the API number, which is the "Unique Well Identifier" within the county where the well was drilled. They are assigned as part of the well permitting process.
View the fourth group of digits in the API number, which is the "Directional Sidetrack Code" for wells that have been sidetracked, or if they have been drilled around a broken drill pipe or casing that has become lodged in the drill hole. The number "03" in the above example means that it was the third sidetracked well in the state where it is located.
Examine the fifth group of digits in the API number, which is the "Event Sequence Code," which indicates how many operations have taken place in a single bore hole. In the above example, "00" indicates that there have been no previous operations in this particular well.