NGA 70 AOCS & Natural Gas Properties
Exam Prep 2025/2026 – Updated Study
Guide
Section 1: Fundamentals and Gas Properties (Questions 1-20)
1. What is the primary constituent of natural gas?
a) Ethane
b) Propane
c) Nitrogen
d) Methane ✓
2. The distinctive odor of natural gas in distribution lines is caused by:
a) Inherent sulfur compounds in the gas
b) The addition of odorants like Mercaptan ✓
c) The combustion process
d) Chemical reactions in the pipeline
3. The specific gravity of natural gas is typically compared to what substance?
a) Water
b) Propane
c) Air ✓
d) Hydrogen
4. If natural gas has a specific gravity of 0.6, this means it is:
a) 60% heavier than air
b) 60% lighter than air ✓
c) The same weight as air
d) 40% lighter than air
5. The Wobbe Index is a key measurement for:
a) Determining the heating value of a gas ✓
b) Measuring gas pressure
c) Calculating gas volume
d) Assessing pipeline corrosion
6. What does the term "BTU" (British Thermal Unit) represent?
a) The volume of gas delivered
,b) The pressure of the gas stream
c) The amount of heat required to raise the temperature of one pound of water by one degree
Fahrenheit ✓
d) The specific gravity of the gas
7. The point at which a hydrocarbon liquid will condense from a gas stream is called the:
a) Flash point
b) Vapor pressure
c) Dew point ✓
d) Bubble point
8. Which hydrocarbon in natural gas is the heaviest?
a) Methane
b) Ethane
c) Propane
d) Pentane ✓
9. The ideal gas law is represented by which formula?
a) P1V1 = P2V2
b) PV = nRT ✓
c) V1/T1 = V2/T2
d) P1/T1 = P2/T2
10. What is "rich" natural gas?
a) Gas with a high concentration of methane
b) Gas with a high concentration of inert gases
c) Gas with a high concentration of natural gas liquids (NGLs) ✓
d) Gas that has been fully odorized
11. The process of removing water vapor from natural gas is known as:
a) Filtration
b) Compression
c) Dehydration ✓
d) Sweetening
12. What is the primary hazard associated with Hydrogen Sulfide (H₂S) in natural gas?
a) It reduces the heating value significantly.
b) It is highly toxic and can be fatal. ✓
c) It causes a foul odor that cannot be masked.
d) It is highly explosive on its own.
,13. Gas that has had H₂S and CO₂ removed is referred to as:
a) Dry gas
b) Lean gas
c) Sweet gas ✓
d) Rich gas
14. The measurement of gas volume at standard conditions (e.g., 14.73 psia, 60°F) is crucial
because:
a) It eliminates the effects of temperature and pressure, allowing for a consistent basis of sale.
✓
b) It is the pressure at which all pipelines operate.
c) It is the easiest volume to measure.
d) It represents the volume inside the pipeline.
15. According to Boyle's Law, if the pressure on a gas is increased, the volume will:
a) Increase
b) Decrease ✓
c) Remain the same
d) Become unpredictable
16. According to Charles's Law, if the temperature of a gas is decreased, the volume will:
a) Increase
b) Decrease ✓
c) Remain the same
d) Fluctuate randomly
17. The combined gas law is a combination of which two laws?
a) Boyle's and Charles's ✓
b) Newton's and Boyle's
c) Charles's and Pascal's
d) Dalton's and Avogadro's
18. What is the purpose of a gas chromatograph in gas measurement?
a) To measure pressure and temperature
b) To separate and analyze the individual components of a gas sample to determine its heating
value and composition ✓
c) To remove liquids from the gas stream
d) To control the pressure of the gas
, 19. The term "Cricondenbar" refers to:
a) The maximum pressure at which two phases can coexist. ✓
b) The minimum temperature for gas liquefaction.
c) The point at which gas becomes odorless.
d) The standard temperature for gas measurement.
20. The heating value of natural gas that includes the latent heat of vaporization of water
vapor in the combustion products is called:
a) Gross Heating Value (GHV) or Higher Heating Value (HHV) ✓
b) Net Heating Value (NHV) or Lower Heating Value (LHV)
c) Wobbe Index
d) Specific Heating Value
Section 2: AOCS Components and Measurement (Questions 21-50)
21. What does the acronym "AOCS" stand for?
a) Automated Operational Control System
b) Automated Odorant and Control Station
c) Automated Odorization, Control, and Safety
d) Automated Odorization & Control System ✓
22. The primary purpose of an AOCS is to:
a) Measure the gas flow rate accurately.
b) Control the pipeline pressure.
c) Inject a precise amount of odorant into the gas stream for safety. ✓
d) Filter out solid particulates from the gas.
23. Which component of an AOCS stores the liquid odorant?
a) Injection Pump
b) Odorant Tank or Storage Vessel ✓
c) Controller
d) Flow Meter
24. The device that provides the mechanical force to inject odorant into the gas stream is the:
a) Odorant Tank
b) Pulse Flow Meter
c) Injection Pump ✓
d) Check Valve
Exam Prep 2025/2026 – Updated Study
Guide
Section 1: Fundamentals and Gas Properties (Questions 1-20)
1. What is the primary constituent of natural gas?
a) Ethane
b) Propane
c) Nitrogen
d) Methane ✓
2. The distinctive odor of natural gas in distribution lines is caused by:
a) Inherent sulfur compounds in the gas
b) The addition of odorants like Mercaptan ✓
c) The combustion process
d) Chemical reactions in the pipeline
3. The specific gravity of natural gas is typically compared to what substance?
a) Water
b) Propane
c) Air ✓
d) Hydrogen
4. If natural gas has a specific gravity of 0.6, this means it is:
a) 60% heavier than air
b) 60% lighter than air ✓
c) The same weight as air
d) 40% lighter than air
5. The Wobbe Index is a key measurement for:
a) Determining the heating value of a gas ✓
b) Measuring gas pressure
c) Calculating gas volume
d) Assessing pipeline corrosion
6. What does the term "BTU" (British Thermal Unit) represent?
a) The volume of gas delivered
,b) The pressure of the gas stream
c) The amount of heat required to raise the temperature of one pound of water by one degree
Fahrenheit ✓
d) The specific gravity of the gas
7. The point at which a hydrocarbon liquid will condense from a gas stream is called the:
a) Flash point
b) Vapor pressure
c) Dew point ✓
d) Bubble point
8. Which hydrocarbon in natural gas is the heaviest?
a) Methane
b) Ethane
c) Propane
d) Pentane ✓
9. The ideal gas law is represented by which formula?
a) P1V1 = P2V2
b) PV = nRT ✓
c) V1/T1 = V2/T2
d) P1/T1 = P2/T2
10. What is "rich" natural gas?
a) Gas with a high concentration of methane
b) Gas with a high concentration of inert gases
c) Gas with a high concentration of natural gas liquids (NGLs) ✓
d) Gas that has been fully odorized
11. The process of removing water vapor from natural gas is known as:
a) Filtration
b) Compression
c) Dehydration ✓
d) Sweetening
12. What is the primary hazard associated with Hydrogen Sulfide (H₂S) in natural gas?
a) It reduces the heating value significantly.
b) It is highly toxic and can be fatal. ✓
c) It causes a foul odor that cannot be masked.
d) It is highly explosive on its own.
,13. Gas that has had H₂S and CO₂ removed is referred to as:
a) Dry gas
b) Lean gas
c) Sweet gas ✓
d) Rich gas
14. The measurement of gas volume at standard conditions (e.g., 14.73 psia, 60°F) is crucial
because:
a) It eliminates the effects of temperature and pressure, allowing for a consistent basis of sale.
✓
b) It is the pressure at which all pipelines operate.
c) It is the easiest volume to measure.
d) It represents the volume inside the pipeline.
15. According to Boyle's Law, if the pressure on a gas is increased, the volume will:
a) Increase
b) Decrease ✓
c) Remain the same
d) Become unpredictable
16. According to Charles's Law, if the temperature of a gas is decreased, the volume will:
a) Increase
b) Decrease ✓
c) Remain the same
d) Fluctuate randomly
17. The combined gas law is a combination of which two laws?
a) Boyle's and Charles's ✓
b) Newton's and Boyle's
c) Charles's and Pascal's
d) Dalton's and Avogadro's
18. What is the purpose of a gas chromatograph in gas measurement?
a) To measure pressure and temperature
b) To separate and analyze the individual components of a gas sample to determine its heating
value and composition ✓
c) To remove liquids from the gas stream
d) To control the pressure of the gas
, 19. The term "Cricondenbar" refers to:
a) The maximum pressure at which two phases can coexist. ✓
b) The minimum temperature for gas liquefaction.
c) The point at which gas becomes odorless.
d) The standard temperature for gas measurement.
20. The heating value of natural gas that includes the latent heat of vaporization of water
vapor in the combustion products is called:
a) Gross Heating Value (GHV) or Higher Heating Value (HHV) ✓
b) Net Heating Value (NHV) or Lower Heating Value (LHV)
c) Wobbe Index
d) Specific Heating Value
Section 2: AOCS Components and Measurement (Questions 21-50)
21. What does the acronym "AOCS" stand for?
a) Automated Operational Control System
b) Automated Odorant and Control Station
c) Automated Odorization, Control, and Safety
d) Automated Odorization & Control System ✓
22. The primary purpose of an AOCS is to:
a) Measure the gas flow rate accurately.
b) Control the pipeline pressure.
c) Inject a precise amount of odorant into the gas stream for safety. ✓
d) Filter out solid particulates from the gas.
23. Which component of an AOCS stores the liquid odorant?
a) Injection Pump
b) Odorant Tank or Storage Vessel ✓
c) Controller
d) Flow Meter
24. The device that provides the mechanical force to inject odorant into the gas stream is the:
a) Odorant Tank
b) Pulse Flow Meter
c) Injection Pump ✓
d) Check Valve
