Vasquez-Beggs Solution Gas-Oil Ratio Calculator
Enter pressure, reservoir temperature, oil API gravity, gas specific gravity, and the Vasquez-Beggs coefficient set for the applicable API range. The output is solution gas-oil ratio in scf/STB.
Enter pressure, reservoir temperature, oil API gravity, gas specific gravity, and the Vasquez-Beggs coefficient set for the applicable API range. The output is solution gas-oil ratio in scf/STB.
Published by PetroCalcHub Team. Linked workflow tools and revision log.
Calculation context and source notes
The Vasquez-Beggs correlation estimates solution gas-oil ratio from pressure, temperature, oil API gravity, gas specific gravity, and the coefficient set selected for the oil-gravity range.
Use the correlation for black-oil PVT screening when laboratory differential-liberation data or a calibrated PVT model are unavailable. Select the API-gravity coefficient range deliberately and compare the estimate with regional fluid data whenever possible.
Harmony oil correlations: Vasquez-Beggs coefficient familiesSolves for
R_s (SCF/STB)
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Formula, variables, and sourceVasquez-Beggs coefficients at 30 API
Select all three coefficients from the same row. The calculator exposes C_rs1, C_rs2 and C_rs3 as editable inputs; changing API alone does not automatically replace their values. At exactly 30 API, use the at-or-below-30 row, not the above-30 row.
| Oil gravity | C1 | C2 | C3 |
|---|---|---|---|
| API <= 30 | 0.0362 | 1.0937 | 25.7240 |
| API > 30 | 0.0178 | 1.1870 | 23.9310 |
Pressure, temperature and gas-gravity basis
Use absolute pressure in psi and enter reservoir temperature in Fahrenheit. The formula applies its own T + 460 conversion; entering Rankine would apply that offset twice. Gas gravity must follow the source's separator/reference basis, not simply whichever gas sample is easiest to obtain.
The output is solution gas per stock-tank barrel in scf/STB. It is not a universal estimate of produced GOR, gas-cap production or storage-tank emissions. The calculator also does not accept bubble-point pressure or impose a constant-Rs branch above it, so establish the pressure regime independently.
Check the coefficient-family calculation
With 2,500 psia, 180 F, 35 API, gas gravity 0.8 and the above-30 coefficients, the calculation is 0.0178 x 0.8 x 2,500^1.187 x exp(23.931 x 35/640) = 569.164106 scf/STB. At 30 API with the at-or-below-30 coefficients, the same pressure, temperature and gas gravity give 503.272569 scf/STB.
These are synthetic substitution checks, not evidence that either predicted Rs fits a particular crude oil. Compare models using compatible inputs in the linked PVT workflow and use measured laboratory data when available.
Compare compatible calculations
Standing vs Vasquez-Beggs PVT ComparisonRelated source-backed guides
Formula, variables, and default calculation
Reproducible default result
With the default values shown below, the calculation returns R_s = 569.164106 SCF/STB. Defaults demonstrate the implementation; they are not recommended field values.
2500
180
35
0.8
0.0178
1.187
23.931
Input definitions
p
psiPressure
T
°FReservoir Temperature
API
APIOil API Gravity
gamma_g
fractionGas Specific Gravity
C_rs1
dimensionlessVasquez-Beggs C1 Coefficient (0.0178 if API > 30; 0.0362 if API <= 30)
C_rs2
dimensionlessVasquez-Beggs C2 Coefficient (1.1870 if API > 30; 1.0937 if API <= 30)
C_rs3
dimensionlessVasquez-Beggs C3 Coefficient (23.931 if API > 30; 25.724 if API <= 30)
Output definitions
R_s
Solution Gas-Oil Ratio
p
Pressure
gamma_g
Gas Specific Gravity
Engineering use, assumptions, and limits
Use the correlation for black-oil PVT screening when laboratory differential-liberation data or a calibrated PVT model are unavailable. Select the API-gravity coefficient range deliberately and compare the estimate with regional fluid data whenever possible.
Assumptions
- Pressure, temperature, API gravity, and gas specific gravity use the field-unit basis of the published correlation.
- The input condition is within the black-oil behavior represented by the correlation.
- The coefficient set matches the selected oil API-gravity range.
Limitations
- An empirical correlation is not a substitute for representative laboratory PVT data.
- Accuracy can degrade for fluids and conditions outside the data range used to develop the correlation.
Common mistakes
- Using gauge pressure where the implementation or comparison requires absolute pressure.
- Selecting the wrong API-gravity coefficient set.
- Using separator gas gravity without applying the source correlation's gas-gravity basis or correction.
Frequently asked questions
What inputs does the Vasquez-Beggs Solution Gas-Oil Ratio from Pressure calculator need?
The calculation uses Pressure (p), Reservoir Temperature (T), Oil API Gravity (API), Gas Specific Gravity (gamma_g), Vasquez-Beggs C1 Coefficient (0.0178 if API > 30; 0.0362 if API <= 30) (C_rs1), Vasquez-Beggs C2 Coefficient (1.1870 if API > 30; 1.0937 if API <= 30) (C_rs2), Vasquez-Beggs C3 Coefficient (23.931 if API > 30; 25.724 if API <= 30) (C_rs3). Enter values on the units shown beside each field.
What result does this calculator return?
The primary result is solution gas-oil ratio in SCF/STB. The formula section shows the declared relationship, variables, and a reproducible default calculation.
What should I check before using the result?
Confirm the unit basis, source applicability, and input quality. An empirical correlation is not a substitute for representative laboratory PVT data. Using gauge pressure where the implementation or comparison requires absolute pressure.
Source and record status
Source metadata identifies the relationship implemented by the calculator. Check the cited edition, unit basis, and scope against the engineering case before operational use.
Vasquez and Beggs 1980 oil PVT correlations, as summarized in IHS Harmony / WellTest documentation and PIPESIM fluid-property documentation.
Open source reference