The Eagle Ford formation
Geology, footprint, and mineral-owner context for the Eagle Ford, drawn from public USGS and state survey sources. Resource figures describe the play as a whole and are not a per-acre value. Every figure on this page is an estimate subject to verification of your specific interest.
Last updated June 2026.
What is the Eagle Ford?
The Eagle Ford is an Upper Cretaceous organic-rich shale and marl that forms one of the largest oil and gas plays in the United States, running across South Texas through Karnes, Gonzales, Dimmit, La Salle, and Webb counties. In its 2018 assessment the USGS estimated the Eagle Ford Group and associated strata to hold a mean of about 8.5 billion barrels of undiscovered, technically recoverable oil and 66 trillion cubic feet of gas, a play-wide figure rather than a per-acre yield.
The Eagle Ford is an Upper Cretaceous (Cenomanian-Turonian) calcareous shale and marl that produces across a broad arc of South Texas. It is both a major source rock and a productive reservoir, and it grades through distinct fluid windows: an oil window in the north and east around Gonzales and Karnes, a volatile-oil and condensate window through Dimmit and La Salle, and a gas-condensate window to the south around Webb. That zonation is the defining feature for a mineral owner, because it determines whether your royalty is paid mostly in oil or mostly in gas, and therefore which commodity price drives your check. Operators have also returned to the overlying Austin Chalk across much of the play. An Eagle Ford royalty is valued on the income the wells actually pay, on the standard income multiple, not on the play-wide resource number.
Eagle Ford geology
- Age and lithology
- Upper Cretaceous (Cenomanian-Turonian) organic-rich calcareous shale and marl, both source rock and reservoir. Source: USGS Gulf Coast assessment.
- Fluid windows
- Grades from an oil window in the north and east (Gonzales, Karnes) through a volatile-oil and condensate window (Dimmit, La Salle) to a gas-condensate window in the south (Webb), which sets the commodity mix of each county's royalties.
- Where it produces
- A broad belt across South Texas: Karnes, Gonzales, Dimmit, La Salle, and Webb counties, with renewed drilling in the overlying Austin Chalk.
How much oil and gas the Eagle Ford holds
In 2018 the USGS assessed the Eagle Ford Group and associated Cenomanian-Turonian strata of the onshore Gulf Coast to hold a mean of about 8.5 billion barrels of undiscovered, technically recoverable oil and 66 trillion cubic feet of natural gas. These are undiscovered play-wide estimates, not proven reserves and not a measure of any individual property.
Source: USGS Fact Sheet 2018-3033 (Eagle Ford Group and associated strata, Gulf Coast).
Counties in the Eagle Ford play
These are the counties and parishes we cover where the Eagle Ford produces. Each links to local value context and the operators active there.
What the Eagle Ford means for your minerals
A resource estimate for a play is not the value of your acreage. Your mineral and royalty interest is valued on the income your wells actually pay, roughly 36 to 72 times your average monthly royalty check, the same as 3 to 6 times your annual royalty. Where you land in that band depends on your wells decline, the operator, your royalty rate, and any undeveloped drilling upside. For the full method and a free on-screen estimate, see what are my mineral rights worth.
The Eagle Ford is part of the Eagle Ford Shale. For the basin-wide value bands and the counties we buy in, see the Eagle Ford Shale page.
Eagle Ford questions
- What is the Eagle Ford shale?
- The Eagle Ford is an Upper Cretaceous organic-rich shale and marl in South Texas that is one of the largest oil and gas plays in the country. It produces across Karnes, Gonzales, Dimmit, La Salle, and Webb counties through distinct oil, condensate, and gas windows.
- Is the Eagle Ford an oil or a gas play?
- Both, depending on location. The Eagle Ford grades from an oil window in the north and east (Gonzales, Karnes) to a gas-condensate window in the south (Webb). Where your tract sits in the play determines whether your royalty is oil-weighted or gas-weighted, and which commodity price drives your check.
- How are Eagle Ford minerals valued?
- An Eagle Ford interest is valued on the income it pays, roughly 36 to 72 times your average monthly royalty check, with oil-window acreage generally pricing above the gas-condensate window. USGS resource figures describe the whole play, not your property. This is an estimate, subject to verification, not an offer.
Sources
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