Enter the total produced oil volume and the total produced gas volume (for the same time period and on a consistent basis—commonly stock-tank/standard conditions) into the calculator to determine the oil to gas ratio.
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Oil to Gas Ratio Formula
The oil to gas ratio (OGR) measures how much oil is produced for a given amount of gas over the same reporting period and on the same measurement basis. In production work, that usually means stock-tank oil volume divided by gas volume reported at standard conditions. This ratio is useful for production reporting, separator test review, trend monitoring, and quickly identifying whether a stream is relatively oil-rich or gas-rich.
OGR = \frac{O}{G}- OGR = oil to gas ratio
- O = total oil volume
- G = total gas volume
If you know any two of the three variables, the calculator can solve for the third.
O = OGR \cdot G
G = \frac{O}{OGR}How to Use the Calculator Correctly
- Use oil and gas volumes from the same time period, such as a day, month, test interval, or forecast step.
- Use a consistent basis. Gas volume should generally be reported at standard conditions rather than actual flowing conditions.
- Select units that match your data, such as barrels and MMscf or cubic meters and cubic meters.
- Interpret the result in context: a larger OGR means more oil is produced per unit of gas.
Common Unit Forms
| Output Unit | Meaning | Typical Use |
|---|---|---|
| bbl/MMscf | Barrels of oil per million standard cubic feet of gas | Useful when gas volumes are large and field data is in U.S. oilfield units |
| bbl/scf | Barrels of oil per standard cubic foot of gas | Direct reciprocal form when comparing against gas-oil ratio in scf/bbl |
| m3/m3 | Cubic meters of oil per cubic meter of gas | Useful in metric reporting when both phases are on a common volume basis |
When both oil and gas are reported in compatible metric volume units, the ratio is numerically expressed as cubic meters per cubic meter. In practice, it is still treated as a production ratio even though the units cancel algebraically.
Oil to Gas Ratio vs. Gas-Oil Ratio
OGR and gas-oil ratio (GOR) describe the same production stream from opposite directions. OGR tells you how much oil you get per unit gas. GOR tells you how much gas you get per unit oil. In petroleum engineering, GOR is often the more commonly reported value, so it is important not to confuse the two.
GOR = \frac{G}{O}OGR = \frac{1}{GOR}The reciprocal relationship above applies when the units are exact reciprocals. For example, if GOR is in scf/bbl, the direct reciprocal gives OGR in bbl/scf. If you want OGR in barrels per million standard cubic feet, scale by one million.
OGR_{bbl/MMscf} = \frac{10^6}{GOR_{scf/bbl}}How to Interpret the Result
- Higher OGR: the stream is more oil-rich relative to gas.
- Lower OGR: the stream is more gas-rich relative to oil.
- Changing OGR over time: may reflect reservoir depletion, completion changes, artificial lift changes, separator conditions, measurement issues, or operating changes.
OGR is descriptive, not automatically economic. A higher value does not always mean a better well because prices, processing costs, gas takeaway, shrinkage, and facility limits all matter.
Example 1
A well produces 1,200 barrels of oil and 0.8 MMscf of gas during the same month. The oil to gas ratio is:
OGR = \frac{1200}{0.8} = 1500 \; bbl/MMscfThis means the well produced 1,500 barrels of oil for each million standard cubic feet of gas during that month.
Example 2
A test reports 35 m3 of oil and 7,000 m3 of gas on a common reporting basis. The ratio is:
OGR = \frac{35}{7000} = 0.005 \; m^3/m^3The inverse gas-oil ratio for the same test is:
GOR = \frac{7000}{35} = 200 \; m^3/m^3Common Mistakes to Avoid
- Using oil volume from one period and gas volume from another period
- Mixing standard gas volume with actual flowing gas volume
- Comparing stock-tank oil against uncorrected separator gas without confirming basis
- Forgetting that MMscf means million standard cubic feet, which changes the numeric value substantially
- Interpreting OGR as GOR and reversing the meaning of the result
- Attempting to calculate the ratio when gas volume is zero, which makes the equation undefined
When This Ratio Is Useful
- Checking daily, monthly, or test production reports
- Comparing wells or completion intervals on a common basis
- Monitoring whether production is becoming more oil-rich or gas-rich over time
- Reviewing separator or facility performance trends
- Estimating one missing variable when the other two are known
Frequently Asked Questions
Can the oil to gas ratio be zero?
Yes. If oil production is zero while gas production is positive, the oil to gas ratio is zero.
Can the oil to gas ratio be negative?
No. Physical production volumes are not negative in normal reporting, so a valid OGR should be zero or positive.
What happens if gas volume is zero?
The calculation is undefined because the denominator is zero. In that situation, the ratio cannot be computed with the standard formula.
Why does the number change when I switch units?
The physical relationship is the same, but the numeric value changes with the unit scale. This is especially noticeable when switching between scf and MMscf, or between U.S. field units and metric units.
Should oil and gas be measured on the same basis?
Yes. For the ratio to be meaningful, both volumes should be reported consistently for the same time interval and with gas referenced to standard conditions where applicable.
