Reserves Are a Statement About PriceNarrow moat

ExxonMobil (XOM) — moat facet

Nineteen point three billion barrels is not a measurement, it is a calculation at an assumed price — and the price changes every year.

ExxonMobil reported 19.3 billion oil-equivalent barrels of proved reserves at the end of 20251. It is the single largest number in the company's filings, it underpins every depletion charge on the income statement, and it is not a physical measurement. It is a calculation made at an assumed price.

Proved reserves at the end of 2025: 19.3 billion barrelsProved developed 12.3 GOEB — 64%Proved undeveloped 7.0 GOEB — 36%ExxonMobil invested $19.0bn in 2025 converting undeveloped reserves into developed.
A third of the reserve base is a plan, and turning it into production costs about nineteen billion dollars a year.

The rule is precise and worth understanding, because it determines how a reserve base behaves. Proved reserves are reported on the basis of the average of the first-day-of-the-month price for each month during the year, and the company notes that prices used in any given year may not represent the price it expects to receive2. A barrel is proved if it can be produced economically at that average. Raise the average and marginal barrels become economic without anybody drilling; lower it and barrels vanish from the books without anybody producing them.

That is why a reserve base is a weak measure of a moat and a good measure of a price cycle. In 2025, with realised Brent at $69.06 against $80.76 the year before3, ExxonMobil removed proved undeveloped reserves that no longer met the SEC definition, primarily in the United States4. Nothing changed underground.

The more meaningful figure inside the total is the split. About 7.0 billion barrels — thirty-six per cent of the 19.3 billion — are classified as proved undeveloped, against 7.4 billion a year earlier, and ExxonMobil invested $19.0 billion in 2025 converting undeveloped reserves into developed ones5. A third of the reserve base is a plan rather than a producing asset, and turning it into production costs real money at a rate of roughly nineteen billion dollars a year.

ExxonMobil's process around this is genuinely rigorous by industry standards — a Global Reserves and Resources group whose endorsement is mandatory for all proved reserves changes, and a requirement that management has made significant funding commitments before a reserve is booked6. That discipline is a reason to trust the number, not a reason to think it means more than it does.

Watch the proportion of reserves that are undeveloped. Thirty-six per cent, falling, on a base of 19.3 billion barrels7 is a company converting inventory into production. Thirty-six per cent, rising, on a base held up by price revisions would be a company booking optimism.

Moat trajectory: Holding steady

The reserve base is 19.3 billion oil-equivalent barrels with thirty-six per cent undeveloped, against thirty-six per cent a year earlier on a slightly larger total. ExxonMobil converts about nineteen billion dollars a year of undeveloped into developed. The number moves with price as much as with drilling, which is why it neither widens nor narrows in any meaningful sense.

The number that tests this moat
Reported
Proved reserves, and how much is undeveloped
19.3 billion barrels, 36% undeveloped

About 7.0 of the 19.3 billion oil-equivalent barrels are proved undeveloped, against 7.4 billion a year earlier, and ExxonMobil invested $19.0 billion in 2025 converting undeveloped into developed. Reserves are calculated at a twelve-month average price, so a falling price removes barrels nobody produced.

Source: Exxon Mobil Corporation Form 10-K, fiscal year 2025 ↗
⚠ Threats to the moat
⚠ THREAT 01
An Extended Period of Low Prices Removes Reserves Nobody Produced
A low price removes barrels nobody produced, raises the depletion charge and triggers the impairment, all in the same quarter cash flow falls.
References
  1. ReportedExxonMobil reported 19.3 billion oil-equivalent barrels of proved reserves at the end of 2025.
    Exxon Mobil Corporation Form 10-K for FY2025, Items 1 and 2 — Business and Properties: oil and gas production and reserves tables, wells drilling, the review of principal ongoing activities by region (United States, Canada/Other Americas incl. Guyana and Brazil, Europe, Africa, Asia, Australia/Oceania), lease and production-sharing terms including the Guyana Petroleum Activities Act 2023, employees, and the list of lower-emission and new business opportunities. — FY2025 · publ. February 2026 · source ↗
  2. ReportedProved reserves are reported on the basis of the average of the first-day-of-the-month price for each month during the year, and the company notes that prices used in any given year may not represent the price it expects to receive.
    Exxon Mobil Corporation Form 10-K for FY2025, Items 1 and 2 — Business and Properties: oil and gas production and reserves tables, wells drilling, the review of principal ongoing activities by region (United States, Canada/Other Americas incl. Guyana and Brazil, Europe, Africa, Asia, Australia/Oceania), lease and production-sharing terms including the Guyana Petroleum Activities Act 2023, employees, and the list of lower-emission and new business opportunities. — FY2025 · publ. February 2026 · source ↗
  3. ReportedIn 2025, with realised Brent at $69.06 against $80.76 the year before, ExxonMobil removed proved undeveloped reserves that no longer met the SEC definition, primarily in the United States.
    Exxon Mobil Corporation Form 10-K for FY2025, Market Risks — worldwide average realisations for Brent, Henry Hub and TTF, and the disclosed sensitivity of Upstream earnings to a one dollar change in Brent, a ten cent change in Henry Hub and a ten cent change in TTF. — FY2025 · publ. February 2026 · source ↗
  4. ReportedIn 2025, with realised Brent at $69.06 against $80.76 the year before, ExxonMobil removed proved undeveloped reserves that no longer met the SEC definition, primarily in the United States.
    Exxon Mobil Corporation Form 10-K for FY2025, Items 1 and 2 — Business and Properties: oil and gas production and reserves tables, wells drilling, the review of principal ongoing activities by region (United States, Canada/Other Americas incl. Guyana and Brazil, Europe, Africa, Asia, Australia/Oceania), lease and production-sharing terms including the Guyana Petroleum Activities Act 2023, employees, and the list of lower-emission and new business opportunities. — FY2025 · publ. February 2026 · source ↗
  5. ReportedAbout 7.0 billion barrels — thirty-six per cent of the 19.3 billion — are classified as proved undeveloped, against 7.4 billion a year earlier, and ExxonMobil invested $19.0 billion in 2025 converting undeveloped reserves into developed ones.
    Exxon Mobil Corporation Form 10-K for FY2025, Items 1 and 2 — Business and Properties: oil and gas production and reserves tables, wells drilling, the review of principal ongoing activities by region (United States, Canada/Other Americas incl. Guyana and Brazil, Europe, Africa, Asia, Australia/Oceania), lease and production-sharing terms including the Guyana Petroleum Activities Act 2023, employees, and the list of lower-emission and new business opportunities. — FY2025 · publ. February 2026 · source ↗
  6. ReportedExxonMobil's process around this is genuinely rigorous by industry standards — a Global Reserves and Resources group whose endorsement is mandatory for all proved reserves changes, and a requirement that management has made significant funding commitments before a reserve is booked.
    Exxon Mobil Corporation Form 10-K for FY2025, Items 1 and 2 — Business and Properties: oil and gas production and reserves tables, wells drilling, the review of principal ongoing activities by region (United States, Canada/Other Americas incl. Guyana and Brazil, Europe, Africa, Asia, Australia/Oceania), lease and production-sharing terms including the Guyana Petroleum Activities Act 2023, employees, and the list of lower-emission and new business opportunities. — FY2025 · publ. February 2026 · source ↗
  7. ReportedThirty-six per cent, falling, on a base of 19.3 billion barrels is a company converting inventory into production.
    Exxon Mobil Corporation Form 10-K for FY2025, Items 1 and 2 — Business and Properties: oil and gas production and reserves tables, wells drilling, the review of principal ongoing activities by region (United States, Canada/Other Americas incl. Guyana and Brazil, Europe, Africa, Asia, Australia/Oceania), lease and production-sharing terms including the Guyana Petroleum Activities Act 2023, employees, and the list of lower-emission and new business opportunities. — FY2025 · publ. February 2026 · source ↗
Sources
Generated September 23, 2026