Oil & Gas
STB vs bbl: What Is the Difference?
Engineers new to petroleum often confuse the Stock Tank Barrel (STB) with the reservoir barrel (RB). An STB is measured at surface standard conditions — 60°F and 14.696 psia. The reservoir barrel accounts for in-situ pressure and temperature, where oil expands. The ratio between them is the Formation Volume Factor (Bo). For typical crude, 1 RB ≈ 1.2–1.5 STB depending on GOR and reservoir conditions. Always confirm which barrel your flow meter reports before converting production data.
Flow Rate
MMSCFD Explained: Gas Flow Rate Conversion
MMSCFD stands for Million Standard Cubic Feet per Day — the most common gas rate unit in US operations and many Middle East field reports. "Standard" means the volume is corrected to 60°F and 14.696 psia. To convert to SI, multiply by 28,316.8 to get Sm³/d. European gas markets often use MNMCD at 0°C / 1.01325 bar — a subtly different standard condition causing a 2–3% discrepancy that matters enormously in LNG contracts and gas sales agreements.
Pressure
PSI, Bar, and MPa: Which Unit to Use When?
The US oilfield uses psi — wellhead pressures range 500 to 15,000 psi. Europe and international projects prefer bar (1 bar ≈ 14.504 psi). Academic and engineering literature increasingly uses MPa from the SI system (1 MPa = 145.04 psi). HPHT wells above 10,000 psi are rated in kpsi. A single unit error in a high-pressure well design can be catastrophic — a 15,000 psi BOP is rated at 103.4 MPa, not 103.4 bar (which would be only 1,500 psi). Our converter handles all systems instantly.
Petrophysics
API Gravity and Crude Oil Density
API gravity is the standard scale used worldwide to express crude oil density. Formula: °API = (141.5 / SG) − 131.5, where SG is specific gravity at 60°F. Light crude (°API > 35) yields more gasoline and diesel and commands premium pricing. Heavy crude (°API < 22) requires more complex refining. Water = 10° API. Knowing API gravity is critical for fiscal metering, pipeline tariffs, and crude selection at refineries. Use our API / Density tab to convert instantly between °API, SG, kg/m³, lb/ft³, and lb/gal.
Reservoir Engineering
Darcy and Millidarcy: Measuring Permeability
Permeability describes how easily fluid flows through reservoir rock. One Darcy allows 1 cm³/s of a 1-centipoise fluid through 1 cm² under a 1 atm/cm pressure gradient. Most real reservoirs are measured in millidarcies (mD): good conventional sandstone 100–500 mD; tight gas sands 0.01–1 mD; shale plays 1–200 nD (nanodarcies). In SI units: 1 mD = 9.869 × 10⁻¹⁶ m². Use the Permeability tab to convert instantly across all scales from nanodarcy to Darcy.
Field Engineering
Metric to Imperial: The Field Engineer's Cheat Sheet
Every field engineer needs these conversions memorised: 1 metre = 3.2808 feet · 1 kilometre = 0.6214 miles · 1 kilogram = 2.2046 pounds · 1 litre = 0.2642 US gallons · 1 bar = 14.504 psi · °F = (°C × 9/5) + 32. These appear daily on drilling rigs, production platforms, and in engineering reports across the Middle East, North Sea, and Americas. This converter gives you all of them instantly with 8-significant-figure precision per ISO 80000 standards.