Two different questions
Gross acres vs. net acres
Gross acres measure the land. Net acres measure your share of it.
Every interest calculation starts by keeping those two ideas apart. The gross acreage is the size of the tract: what a surveyor would measure. Your net mineral acres are that number scaled down by the fraction of the minerals you actually own:
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One caution before the math gets rolling: that picture is a teaching convenience. An undivided 1/4 interest isn't a fenced-off quarter of the tract: it's a 1/4 share of every acre, including whatever the well finds under any of them.
Your fractional mineral ownership expressed in acres: fraction owned × gross acres in the tract. The industry's standard unit for buying, selling, and leasing mineral interests: bonus is quoted per NMA.
Your share, in acres
Calculating net mineral acres
In real chains the fraction isn't handed to you: it accumulates over generations of conveyances. The method: walk the chain and multiply.
Step 3 hides the most important reading skill in mineral math. Compare:
- "1/4 of the minerals": a fraction of the whole mineral estate. Cora would get 1/4, leaving Ben just 1/4.
- "1/4 of my interest": a fraction of what the grantor owns. Cora gets 1/4 × 1/2 = 1/8, and Ben keeps 3/8.
Same little fraction, completely different outcomes. When examiners argue about a deed, it's very often about what the fraction is a fraction of.
"Every mineral fraction is a fraction of something. Find the something."
The money decimal
Working interest & net revenue interest
NMA measures what you own. The net revenue interest (NRI) measures what you're paid: your decimal share of each production dollar. They're related but not the same, because the lease splits every dollar between two camps:
- The working interest (WI), the lessee's side: the right to develop, and the duty to pay all the costs.
- The royalty side: the lessor (and anyone else holding a royalty) takes a share of revenue free of those costs.
For a royalty owner, the equation is three numbers long:
The working interest has its own version. The lessee receives whatever's left after the royalty burdens come off the top. With a 1/4 royalty and no other burdens, a 100% working interest keeps an NRI of 1 − 0.25 = 0.75. Which brings us to the things that eat into that number…
The burden stack
Overriding royalties & NPRIs
Two more characters take their cut of the revenue dollar, and both should look familiar from Topics 01 and 02:
- An overriding royalty interest (ORRI) is carved out of the lease: typically by a landman, geologist, or prior lessee assigning the lease and keeping "an override." It's a cost-free slice of production that lives and dies with that lease.
- A non-participating royalty interest (NPRI) is carved out of the mineral estate itself: stick five from Topic 01, severed by deed. It survives any particular lease and burdens the mineral owner's royalty.
The arithmetic is pure subtraction: WI NRI = WI share × (1 − all royalty burdens). The drama is in the stacking: an old NPRI, a negotiated 1/4 royalty, two overrides from prior assignments, and suddenly the operator's 0.75 is 0.68 and somebody's deal just got thinner.
Who bears an NPRI? Generally it comes out of the royalty of the mineral interest it was carved from, which is why an examiner has to know not just that an NPRI exists, but whose share it burdens. Drafting and state law both matter here; flag it, don't wing it.
Sharing the well
Pooling & unit math
Topic 03 introduced pooling: several tracts combined into one drilling unit, sharing one well. The money question (how much of the well does each owner get?) has a standard answer: by acreage contribution.
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← you're here
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Note what pooling did to the equation from Fig. 3: nothing. It just redefined the denominator. Your NMA in the unit over the unit's total acres, times your royalty. The well can be on your tract or your neighbor's: the math doesn't care.
Real units get messier: tracts can contribute partially, and some states' regulatory units allocate production on factors other than straight acreage. The acreage-proration version here is the standard mental model; learn it cold and the variations will make sense.
Pencil out
Worked examples: simple, messy, ugly
Three problems, every step shown. Work each one yourself before reading the steps: that's the whole point.
Sam owns 40 NMA in a tract fully inside a 320-acre unit, leased at 1/8 royalty. What's Sam's decimal?
Grandma owned 1/2 the minerals under 240 acres. Her interest passed equally to 3 grandkids; you're one of them. You lease at 3/16, and the whole tract goes into a 640-acre unit. Your decimal?
Dee owns 1/4 of the minerals under a 320-acre tract, but only 160 acres of that tract fall inside the 640-acre unit. Lease royalty: 1/4. Dee's decimal in this unit's well?
Notice the ugly one landed on the same decimal as the simple one. Fractions don't care how hard the path was, which is exactly why you show your steps: two owners with identical decimals can have completely different titles behind them.
Where the money lands
Division orders & the decimal interest
All of this arithmetic funnels into one document. Before a well's revenue gets distributed, the payor sends each owner a division order, a statement of the owner's decimal, to be confirmed and signed:
Two habits to build now:
- Check the decimal yourself. The payor's title department is good, but they're working from the same messy records you are. If your math says 0.01171875 and the division order says 0.01071875, somebody's wrong: find out who before signing.
- A division order confirms; it shouldn't convey. It's an accounting document, not a deed. Signing one generally doesn't change your underlying ownership, though what happens if you sign a wrong one varies by state, which is one more reason to check the number.
And with that, you can do something genuinely rare: read a chain of fractions and turn it into the exact decimal on a real check. The last topic puts this skill to work at full scale: examining title from the patent forward.
Test yourself
Quick gut-check
Three quick ones: pencil encouraged. Tap to check yourself.