Sources and methods

The data series

EIA is the U.S. Energy Information Administration. The decline chart in Chapter 3 is an illustration, not data, and uses none of these series.

How we collect it

Bedrock, Basin Ventures' data system, downloads the EIA series through the EIA's public data service every Friday and the CPI from FRED each month. Every download is recorded with the date it was taken, so when the EIA revises a past number, both versions are kept and the pages use the latest one.

How we calculate

• Monthly figures from weekly data: the average of the weekly values whose week ends in that month. A month is shown only once it is complete.
• Natural gas per day: each month's total production divided by the number of days in the month, then converted from million to billion cubic feet.
• Today's dollars: a month's price multiplied by the latest CPI divided by that month's CPI. Each chapter names the CPI month it uses. Weekly prices after the latest CPI month are shown at the time.
• Annual figures: the average of the monthly figures. A year that is not complete is labeled with the months it covers.
• Records and comparisons, such as "higher than about three in four months since 1986", are calculated on monthly averages, in today's dollars where prices are involved.
• Rounding: prices to the cent, oil production to two decimals in millions of barrels a day, and gas production to one decimal in billion cubic feet a day. Summary figures in the text, such as "about $76", are rounded from those.

Known gaps and limits

• There is no CPI value for October 2025 in the FRED series, so that month is left out of inflation-adjusted figures and of the 2025 price averages.
• The EIA's weekly oil production numbers are estimates. Its later monthly figures, based on surveys of operators, can differ slightly.
• The EIA revises past values from time to time. These pages use the latest published figures.
• Benchmark prices are reference prices. They are not the price any particular producer receives, which depends on location, quality and transport.
• Some series start later than others: Henry Hub prices and dry gas production in this guide begin in 1997, crude oil prices in 1986 and crude oil production in 1983.