3.4. Methodology for Estimating CH4 and CO2 Emissions from Natural Gas Systems 

The following steps were used to estimate CH4 and non-energy CO2 emissions from natural gas systems. 

Step 1: Calculate Emission Estimates for Base Year 1992 Using EPA Adjusted GRI/EPA Study 

The first step in estimating CH4 and non-energy related (i.e., fugitive, vented and flared) CO2 emissions from 

natural gas systems was to develop a detailed base year estimate of emissions. The study by EPA/GRI (1996) divides the 

industry into four stages to construct a detailed emission inventory for the year 1992. These stages include: field 

production, processing, transmission and storage (i.e., both underground and liquefied gas storage), and distribution. This 

study produced emission factors and activity data for over 80 different emission sources within the natural gas system. 

Emissions for 1992 were estimated by multiplying activity levels by emission factors for each system component and then 

summing by stage. Since publication, the EPA has updated activity data for some of the components in the system based 

on publicly available data. For other sources where annual activity data are not available, a set of industry activity factor 

drivers was developed that can be used to update activity data. Table A- 118 through Table A- 121 display the 2008 

activity levels, CH4 emission factors, and CH4 emissions for each stage.. These data are shown to illustrate the kind of 

data used to calculate CH4 and non-energy CO2 emissions from all stages. For most sources, the CH4 emission factors 

were adjusted for CO2 content when estimating fugitive and vented non-energy CO2 emissions. In the case of non-energy 

CO2 emissions from flared sources, acid gas removal units and condensate tanks, specific industry data related to those 

sources was used to derive their respective emission factors. 

The activity levels and CH4 emission factors in Table A- 118 are arranged into regions designated by the 

National Energy Modeling System (NEMS). NEMS splits the continental United States into 6 regions: Northeast, MidCentral, Rocky Mountain, South West, West Coast and Gulf Coast. GRI, however, does not evaluate activity data for each 

of these regions separately. The GRI national AF estimates were allocated to the NEMS regions using the NEMS regional 

gas well counts to national well count ratios. 

Step 2: Collect Aggregate Statistics on Main Driver Variables 

As detailed data on each of the over 80 sources were not available for the period 1990 through 2008, activity 

levels were estimated using aggregate statistics on key drivers, including: number of producing wells (EIA 2009a-b, New 

Mexico 2009a-b, Texas 2009a-b), number of gas plants (AGA 1991-1997; OGJ 1998-2009), number of shallow and deep 

offshore platforms (MMS 2009a-d), miles of transmission pipeline (OPS 2009a), miles of distribution pipeline (OPS 

2009b), miles of distribution services (OPS 2009b), and energy consumption (EIA 2009c). 

A-149 
 

 

 

Table A- 122 provides the activity levels of some of the key drivers in the natural gas analysis. 

Step 3: Estimate CH4 Emissions for Each Year and Stage 

Emissions from each stage of the natural gas industry were estimated by multiplying the activity factors by the 

appropriate emission factors, summing all sources for each stage and then accounting for CH4 reductions reported to the 

Natural Gas STAR Program and CH4 reductions resulting from National Emission Standards for Hazardous Air Pollutants 

(NESHAP) regulations. 

Industry partners report CH4 emission reductions by project to the Natural Gas STAR Program. The reductions 

are estimates using actual measurement data or equipment-specific emission factors. Before incorporating the reductions 

into the Inventory, quality assurance and quality control checks are undertaken to identify errors, inconsistencies, or 

irregular data. The checks include matching Natural Gas STAR reported reductions to specific inventory sources to make 

sure that a reported reduction for one source is not greater than the emission estimate for that source. Total emissions were 

estimated by adding the emission estimates from each stage. The base year of the inventory is 1992; therefore any 

reductions reported for 1992 or earlier are considered to be already included in the base-year emission factors and are not 

subtracted from the inventory estimate. If the reported reduction occurred between 1990 and 1992, then the reduction is 

added back into the estimate for the appropriate year(s). The reductions are also adjusted to remove the sunsetting time 

period which is relevant to Natural Gas STAR accounting but not the Inventory. For example, replacing a gas-assisted 

pump with an electric pump permanently reduces the vented methane emissions from that source, even after the Natural 

Gas STAR sunsetting period. CH4 emission reductions from the Natural Gas STAR Program beyond the efforts reflected 

in the 1992 base year are summarized in Table A- 123. 

The 1990 Clean Air Act (CAA) sets the limits on the amount of hazardous air pollutants (HAPs) that can be 

emitted in the United States. The NESHAP regulations set the standards to limit emissions of HAPs. The emission sources 

are required to use the Maximum Achievable Control Technology, giving the operators flexibility to choose the type of 

control measure(s) to implement. In regards to the oil and natural gas industry, the NESHAP regulation addresses HAPs 

from the oil and natural gas production sectors and the natural gas transmission and storage sectors of the industry. 

Though the regulation deals specifically with HAPs reductions, methane emissions are also reduced. 

The NESHAP regulation requires that glycol dehydration unit vents and storage tanks that have HAP emissions 

and exceed a gas throughput and liquids throughput value, respectively, be connected to a closed loop emission control 

system that reduces emissions by 95 percent. Also, gas processing plants exceeding the threshold natural gas throughput 

limit are required to routinely implement Leak Detection and Survey (LDAR) programs. The emissions reductions 

achieved as a result of NESHAP regulations were estimated using data provided in the Federal Register Background 

Information Document (BID) for this regulation. The BID provides the levels of control measures in place before the 

enactment of regulation. The emissions reductions were estimated by analyzing the portion of the industry without control 

measures already in place that would be impacted by the regulation. The reductions are representative of the control 

measures in both the oil and natural gas industry. CH4 emission reductions from the NESHAP regulation are summarized 

in Table A- 124. 

Step 4: Estimate CO2 Emissions for Each Year and Stage 

The same procedure for estimating CH4 emissions holds true for estimating non-energy related CO2 emissions, 

except the emission estimates are not corrected for reductions due to the Natural Gas STAR program or the NESHAP 

regulations. 

Produced natural gas is composed of primarily CH4, but as shown in Table A- 129, the natural gas contains, in 

some cases, as much as 8 percent CO2. The same vented and fugitive emissions of natural gas that led to CH4 emissions 

also contain a certain volume of CO2. Accordingly, the CO2 emissions for each sector can be estimated using the same 

methane activity and emissions factors for these vented and fugitive sources. The primary difference is that EPA/GRI 

emission factors are adjusted for CO2 content in each sector. 

 Using the default CH4 content of produced natural gas from EPA/GRI (1996) of 78.8 percent, the corresponding 

amount of CO2 emissions from the production sector can be estimated. Each sector of the natural gas system has varying 

CO2 contents, similar to the way the CH4 content varies among the sectors. Table A- 129 shows the CO2 content for the 

different well types in the production sector of the natural gas system. In the estimation of CO2 emissions from the 

production sector, the production sector CH4 emission factors were used as a basis to estimate CO2 emissions; however, 

they were converted to CO2 emission factors by multiplication by a conversion factor. This conversion factor is the ratio 

of CO2 content in the gas stream (in this case the production concentrations provided in Table A- 129) to the 

corresponding CH4 content of the same gas stream. The three exceptions to this methodology are CO2 emissions from 

A-142 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2008 
 

 

 

flares, acid gas removal units, and condensate tanks. In the case of flare emissions, a direct CO2 emission factor from EIA 

(1996) was used. This emission factor was applied to the portion of offshore gas that is not vented and all of the gas 

reported as vented and flared onshore by EIA. The amount of CO2 emissions from an acid gas unit in a processing plant is 

equal to the difference in CO2 concentrations between produced natural gas and pipeline quality gas applied to the 

throughput of the plant. This methodology was applied to the national gas throughput using national average CO2 

concentrations in produced gas (3.45 percent) and transmission quality gas (1 percent). For condensate tanks, a series of 

API Tankcalc (EPA 1999) simulations provide the total CO2 vented per barrel of condensate throughput from fixed roof 

tank flash gas for condensate gravities of API 44 degree and higher. The ratios of emissions to throughput were used to 

estimate the CO2 emission factor for condensate passing through fixed roof tanks. The detailed source emission estimates 

for CH4 and CO2 from the production sector are presented in Table A- 125 and Table A- 130, respectively. 

In the processing sector, the CO2 content of the natural gas remains the same as the CO2 content in the 

production sector for the equipment upstream of the acid gas removal unit because produced natural gas is usually only 

minimally treated after being produced and then transported to natural gas processing plants via gathering pipelines. The 

CO2 content in gas for the remaining equipment that is downstream of the acid gas removal is the same as in pipeline 

quality gas. The EPA/GRI study estimates the average CH4 content of natural gas in the processing sector to be 87 percent 

CH4. Consequently, the processing sector CH4 emission factors were proportioned to reflect the CO2 content of either 

produced natural gas or pipeline quality gas using the same methodology as the production sector. The detailed source 

emission estimates for CH4 and CO2 from the processing sector are presented in Table A- 126 and Table A- 131, 

respectively. 

For the transmission sector, CO2 content in natural gas transmission pipelines was estimated for the top twenty 

transmission pipeline companies in the United States (separate analyses identified the top twenty companies based on gas 

throughput and total pipeline miles). The weighted average CO2 content in the transmission pipeline quality gas in both 

cases—total gas throughput and total miles of pipeline—was estimated to be about 1 percent. To estimate the CO2 

emissions for the transmission sector the CH4 emission factors were proportioned from the 93.4 percent CH4 reported in 

EPA/GRI (1996) to reflect the 1 percent CO2 content found in transmission quality natural gas. The detailed source 

emissions estimates for CH4 and CO2 for the transmission sector are presented in Table A- 127 and Table A- 132, 

respectively. 

The natural gas in the distribution sector of the system has the same characteristics as the natural gas in the 

transmission sector. The CH4 content (93.4 percent) and CO2 content (1 percent) are identical due to the absence of any 

further treatment between sector boundaries. Thus, the CH4 emissions factors were converted to CO2 emission factors 

using the same methodology as discussed for the transmission sector. The detailed source emission estimates for CH4 and 

CO2 for the distribution sector are presented in Table A- 128 and Table A- 133, respectively. 

Because Partners report only CH4 emission reductions to the Natural Gas STAR Program, there was no need to 

adjust for the Natural Gas STAR program in the CO2 emissions estimates for any of the sectors in the natural gas system. 

The impact of NESHAP regulations on CO2 emission reductions are not currently addressed in the CO2 emission 

estimates. 

A-143 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table A- 118: 2008 Data and CH4 Emissions (Mg) for the Natural Gas Production Stage 

Activity 

2008 EPA Inventory Values 

Activity Data Emission Factor Emissions 

North East 

Gas Wells 

NE - Associated Gas Wells2 

NE - Non-associated Gas Wells (less 

Unconventional)

NE - Unconventional Gas Wells 

Field Separation Equipment 

Heaters

Separators

Dehydrators

Meters/Piping

Gathering Compressors 

Small Reciprocating Comp. 

Large Reciprocating Comp. 

Large Reciprocating Stations 

Pipeline Leaks 

Drilling and Well Completion 

Completion Flaring 

Well Drilling 

Normal Operations 

Pneumatic Device Vents 

Chemical Injection Pumps 

Kimray Pumps 

Dehydrator Vents 

Condensate Tank Vents 

Condensate Tanks without Control Devices 

Condensate Tanks with Control Devices 

Compressor Exhaust Vented 

Gas Engines 

Well Workovers 

Gas Wells 

Well Clean Ups (LP Gas Wells) 

Blowdowns 

Vessel BD 

Pipeline BD 

Compressor BD 

Compressor Starts 

Upsets 

Pressure Relief Valves 

Mishaps 

Mid-Central 

Gas Wells 

MC - Associated Gas Wells2 

MC - Non-associated Gas Wells 

MC - Unconventional Gas Wells 

Field Separation Equipment 

Heaters

Separators

Dehydrators

Meters/Piping

Gathering Compressors 

Small Reciprocating Comp. 

Large Reciprocating Comp. 

Large Reciprocating Stations 

Pipeline Leaks 

Drilling and Well Completion 

Completion Flaring 

Well Drilling 

Normal Operations 

Pneumatic Device Vents 

Chemical Injection Pumps 

47,088 wells NA 

 174,609 wells 7 scfd/well

0 wells NA scfd/well 

 349 heaters 14 scfd/heater 

 123,972 separators 1 scfd/sep 

 1,130 dehydrators 22 scfd/dehy 

 8,868 meters 9 scfd/meter 

175 compressors 269 scfd/comp 

24 compressors 15,262 scfd/comp 

3 stations 8,278 scfd/station 

84,210 miles 53 scfd/mile

253 completions/year 736 scf/comp 

15,490 wells 2,553 scf/well 

84,860 controllers 346 scfd/device

873 active pumps 249 scfd/pump 

330,819 MMscf/yr 996 scf/MMscf 

371,290 MMscf/yr 277 scf/MMscf 

0 MMbbl/yr 22 scf/bbl

0 MMbbl/yr 4 scf/bbl

0 MMHPhr 0.2 scf/HPhr 

7,595 workovers/yr 2,463 scfy/w.o. 

72,288 LP Gas Wells 49,756 scfy/LP well 

125,452 vessels 78 scfy/vessel 

84,210 miles (gathering) 310 scfy/mile 

175 compressors 3,788 scfy/comp 

175 compressors 8,475 scfy/comp 

334,935 PRV 34 scfy/PRV 

21,053 miles 672 scf/mile 

72,487 wells NA 

70,098 wells 7 scfd/well 

12,702 wells 5 scfd/well 

 33,617 heaters 15 scfd/heater 

 36,018 separators 1 scfd/sep 

 12,027 dehydrators 96 scfd/dehy 

 113,257 meters 9 scfd/meter 

9,356 compressors 282 scfd/comp 

16 compressors 16,013 scfd/comp 

2 stations 8,685 scfd/station 

65,703 miles 56 scfd/mile 

120 completions/year 772 scf/comp 

7,346 wells 2,678 scf/well 

128,423 controllers 363 scfd/device

11,758 active pumps 261 scfd/pump 

NA 

8,774 

NA 

35 

786 

173 

564 

330 

2,575 

175 

 31,583 

4 

762 

 206,584 

1,528 

6,344 

1,978 

­

­

-

360 

69,274 

189 

503 

13 

29 

220 

272 

NA 

3,688 

453 

3,537 

240 

8,114 

7,555 

18,547 

1,801 

122 

25,854 

2 

379 

 328,011 

21,587 

A-144 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2008 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Activity 

2008 EPA Inventory Values 

Activity Data Emission Factor Emissions 

Kimray Pumps 

Dehydrator Vents 

Condensate Tank Vents 

Condensate Tanks without Control Devices 

Condensate Tanks with Control Devices 

Compressor Exhaust Vented 

Gas Engines 

Well Workovers 

Gas Wells 

Well Clean Ups (LP Gas Wells) 

Blowdowns 

Vessel BD 

Pipeline BD 

Compressor BD 

Compressor Starts 

Upsets 

Pressure Relief Valves 

Mishaps 

Rocky Mountain

Gas Wells 

RM - Associated Gas Wells2 

RM - Non-associated Gas Wells 

RM - Unconventional Gas Wells 

Field Separation Equipment 

Heaters

Separators

Dehydrators

Meters/Piping

Gathering Compressors 

Small Reciprocating Comp. 

Large Reciprocating Comp. 

Large Reciprocating Stations 

Pipeline Leaks 

Drilling and Well Completion 

Completion Flaring1

Well Drilling 

Normal Operations 

Pneumatic Device Vents 

Chemical Injection Pumps 

Kimray Pumps 

Dehydrator Vents 

Condensate Tank Vents 

Condensate Tanks without Control Devices 

Condensate Tanks with Control Devices 

Compressor Exhaust Vented 

Gas Engines 

Well Workovers 

Gas Wells 

Well Clean Ups (LP Gas Wells) 

Blowdowns 

Vessel BD 

Pipeline BD 

Compressor BD 

Compressor Starts 

Upsets 

Pressure Relief Valves 

Mishaps 

Coal Bed Methane

 Powder River 

South West 

Gas Wells 

SW - Associated Gas Wells2 

3,520,338 MMscf/yr 1,045 scf/MMscf 

3,950,997 MMscf/yr 290 scf/MMscf 

11 MMbbl/yr 22 scf/bbl 

11 MMbbl/yr 4 scf/bbl 

15,483 MMHPhr 0.3 scf/HPhr 

3,602 workovers/yr 2,584 scfy/w.o. 

34,279 LP Gas Wells 52,203 scfy/LP well 

81,662 vessels 82 scfy/vessel 

65,703 miles (gathering) 325 scfy/mile 

9,356 compressors 3,974 scfy/comp 

9,356 compressors 8,891 scfy/comp 

158,828 PRV 36 scfy/PRV 

16,426 miles 705 scf/mile 

14,630 wells NA 

62,958 wells 36 scfd/well 

25,512 wells 7 scfd/well 

 40,342 heaters 58 scfd/heater

 44,146 separators 122 scfd/sep 

 12,851 dehydrators 91 scfd/dehy 

 102,226 meters 53 scfd/meter 

9,820 compressors 267 scfd/comp 

32 compressors 15,161 scfd/comp 

4 stations 8,223 scfd/station 

113,453 miles 53 scfd/mile 

 128 completions/year 731 scf/comp 

7,849 wells 2,536 scf/well 

129,520 controllers 344 scfd/device

15,748 active pumps 247 scfd/pump 

3,761,376 MMscf/yr 989 scf/MMscf 

4,221,522 MMscf/yr 275 scf/MMscf 

13 MMbbl/yr 22 scf/bbl 

13 MMbbl/yr 4 scf/bbl 

16,543 MMHPhr 0.2 scf/HPhr 

3,848 workovers/yr 2,447 scfy/w.o. 

36,626 LP Gas Wells 49,426 scfy/LP well 

97,339 vessels 78 scfy/vessel 

113,453 miles (gathering) 308 scfy/mile 

9,820 compressors 3,763 scfy/comp 

9,820 compressors 8,418 scfy/comp 

169,702 PRV 34 scfy/PRV 

28,363 miles 667 scf/mile 

28,486,776,948 gal produced water 2.002E-09 

Gg/gallon water 

drainage

55,251 wells NA 

70,832 

22,086 

4,423 

885 

75,370 

179 

34,465 

129 

412 

716 

1,602 

110 

223 

NA 

15,802 

1,244 

16,321 

37,757 

8,209 

37,908 

18,430 

3,411 

231 

42,269 

2 

383 

 313,213 

27,375 

71,656 

22,343 

5,265 

1,053 

76,246 

181 

34,866 

146 

673 

712 

1,592 

111 

364 

57,039 

NA 

A-145 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Activity 

2008 EPA Inventory Values 

Activity Data Emission Factor Emissions 

SW - Non-associated Gas Wells 

SW - Unconventional Gas Wells 

Field Separation Equipment 

Heaters

Separators

Dehydrators

Meters/Piping

Gathering Compressors 

Small Reciprocating Comp. 

Large Reciprocating Comp. 

Large Reciprocating Stations 

Pipeline Leaks 

Drilling and Well Completion 

Completion Flaring1 

Well Drilling 

Normal Operations 

Pneumatic Device Vents 

Chemical Injection Pumps 

Kimray Pumps 

Dehydrator Vents 

Condensate Tank Vents 

Condensate Tanks without Control Devices 

Condensate Tanks with Control Devices 

Compressor Exhaust Vented 

Gas Engines 

Well Workovers 

Gas Wells 

Well Clean Ups (LP Gas Wells) 

Blowdowns 

Vessel BD 

Pipeline BD 

Compressor BD 

Compressor Starts 

Upsets 

Pressure Relief Valves 

Mishaps 

West Coast 

Gas Wells 

WC - Associated Gas Wells2 

WC - Non-associated Gas Wells 

WC - Unconventional Gas Wells 

Field Separation Equipment 

Heaters

Separators

Dehydrators

Meters/Piping

Gathering Compressors 

Small Reciprocating Comp. 

Large Reciprocating Comp. 

Large Reciprocating Stations 

Pipeline Leaks 

Drilling and Well Completion 

Completion Flaring1 

Well Drilling 

Normal Operations 

Pneumatic Device Vents 

Chemical Injection Pumps 

Kimray Pumps 

Dehydrator Vents 

Condensate Tank Vents 

Condensate Tanks without Control Devices 

Condensate Tanks with Control Devices 

Compressor Exhaust Vented 

Gas Engines 

27,903 wells 37 scfd/well 

10,146 wells NA 

 10,311 heaters 59 scfd/heater 

 21,383 separators 125 scfd/sep 

 5,527 dehydrators 93 scfd/dehy 

 46,589 meters 54 scfd/meter 

5,175 compressors 274 scfd/comp 

16 compressors 15,536 scfd/comp 

2 stations 8,426 scfd/station 

56,981 miles 54 scfd/mile 

55 completions/year 749 scf/comp 

3,375 wells 2,598 scf/well 

50,529 controllers 352 scfd/device

2,321 active pumps 253 scfd/pump 

1,617,679 MMscf/yr 1,014 scf/MMscf 

1,815,576 MMscf/yr 282 scf/MMscf 

6 MMbbl/yr 22 scf/bbl 

6 MMbbl/yr 4 scf/bbl 

7,115 MMHPhr 0.2 scf/HPhr 

1,655 workovers/yr 2,507 scfy/w.o. 

15,752 LP Gas Wells 50,648 scfy/LP well 

37,221 vessels 80 scfy/vessel 

56,981 miles (gathering) 316 scfy/mile 

5,175 compressors 3,856 scfy/comp 

5,175 compressors 8,627 scfy/comp 

72,985 PRV 35 scfy/PRV 

14,245 miles 684 scf/mile 

24,259 wells NA 

1,693 wells 42 scfd/well

0 wells NA 

 1,693 heaters 67 scfd/heater 

 1,236 separators 142 scfd/sep 

 246 dehydrators 106 scfd/dehy 

 3,242 meters 62 scfd/meter 

1,966 compressors 312 scfd/comp 

8 compressors 17,728 scfd/comp 

1 stations 9,615 scfd/station 

16,263 miles 62 scfd/mile 

2 completions/year 855 scf/comp 

150 wells 2,965 scf/well 

1,696 controllers 402 scfd/device

1,150 active pumps 289 scfd/pump 

71,980 MMscf/yr 1,157 scf/MMscf 

80,785 MMscf/yr 321 scf/MMscf 

0 MMbbl/yr 22 scf/bbl 

0 MMbbl/yr 4 scf/bbl 

317 MMHPhr 0.3 scf/HPhr 

7,303.98 

NA 

4,274.52 

18,740.61 

3,617.63 

17,703.68 

9,951.73 

1,747.41 

118.47 

21,753.84 

0.80 

169 

 125,212 

4,134 

31,579 

9,847 

2,527 

505 

33,602 

80 

15,366 

57 

346 

384 

860 

49 

188 

NA 

506 

NA 

801 

1,236 

184 

1,406 

4,314 

997 

68 

7,085 

0.04 

9 

4,797 

2,337 

1,603 

500 

-

-

1,706 

A-146 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2008 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Activity 

2008 EPA Inventory Values 

Activity Data Emission Factor Emissions 

Well Workovers 

Gas Wells 

Well Clean Ups (LP Gas Wells) 

Blowdowns 

Vessel BD 

Pipeline BD 

Compressor BD 

Compressor Starts 

Upsets 

Pressure Relief Valves 

Mishaps 

Gulf Coast 

Gas Wells 

GC - Associated Gas Wells2 

GC - Non-associated Gas Wells 

GC - Unconventional Gas Wells 

Field Separation Equipment 

Heaters

Separators

Dehydrators

Meters/Piping

Gathering Compressors 

Small Reciprocating Comp. 

Large Reciprocating Comp. 

Large Reciprocating Stations 

Pipeline Leaks 

Drilling and Well Completion 

Completion Flaring 

Well Drilling 

Normal Operations 

Pneumatic Device Vents 

Chemical Injection Pumps 

Kimray Pumps 

Dehydrator Vents 

Condensate Tank Vents 

Condensate Tanks without Control Devices 

Condensate Tanks with Control Devices 

Compressor Exhaust Vented 

Gas Engines 

Well Workovers 

Gas Wells 

Well Clean Ups (LP Gas Wells) 

Blowdowns 

Vessel BD 

Pipeline BD 

Compressor BD 

Compressor Starts 

Upsets 

Pressure Relief Valves 

Mishaps 

Coal Bed Methane

 Black Warrior 

Offshore Platforms 

Shallow water Gas Platforms (GoM and Pacific) 

Deepwater Gas Platforms (GoM and Pacific) 

74 workovers/yr 2,861 scfy/w.o. 

701 LP Gas Wells 57,796 scfy/LP well 

3,175 vessels 91 scfy/vessel 

16,263 miles (gathering) 360 scfy/mile 

1,966 compressors 4,400 scfy/comp 

1,966 compressors 9,844 scfy/comp 

3,248 PRV 40 scfy/PRV 

4,066 miles 780 scf/mile 

26,560 wells NA 

69,394 wells 41 scfd/well 

0 wells NA scfd/well 

 15,544 heaters 65 scfd/heater 

 45,661 separators 137 scfd/sep 

 10,080 dehydrators 102 scfd/dehy 

 80,993 meters 59 scfd/meter 

5,621 compressors 301 scfd/comp 

24 compressors 17,084 scfd/comp 

3 stations 9,266 scfd/station 

92,088 miles 60 scfd/mile 

101 completions/year 824 scf/comp 

6,156 wells 2,857 scf/well 

48,229 controllers 388 scfd/device

2,290 active pumps 279 scfd/pump 

2,950,362 MMscf/yr 1,115 scf/MMscf 

3,311,293 MMscf/yr 310 scf/MMscf 

32 MMbbl/yr 22 scf/bbl

32 MMbbl/yr 4 scf/bbl

12,976 MMHPhr 0.3 scf/HPhr 

3,019 workovers/yr 2,757 scfy/w.o. 

28,729 LP Gas Wells 55,697 scfy/LP well 

71,286 vessels 88 scfy/vessel 

92,088 miles (gathering) 347 scfy/mile 

5,621 compressors 4,240 scfy/comp 

5,621 compressors 9,487 scfy/comp 

133,112 PRV 38 scfy/PRV 

23,022 miles 752 scf/mile 

5,026 wells 0.002 Gg/well 

2,218 

Shallow water gas 

platforms 19,178 scfd/platform

39 

Deepwater gas 

platforms 79,452 scfd/platform

4 

780 

6 

113 

167 

373 

2 

61 

NA 

19,975 

NA 

7,086 

44,008 

7,256 

33,845 

11,888 

2,882 

195 

38,662 

2 

339 

 131,429 

4,486 

63,337 

19,749 

13,479 

2,696 

67,395 

160 

30,818 

120 

616 

459 

1,027 

98 

333 

11,687 

299,058 

21,783 1 Emissions are not actually 0, but too small to show at this level of precision.
 2 Emissions from oil wells that produce associated gas are estimated in the Petroleum Systems model. Here the oil wells count is used as a driver only. 3 NA = not available; i.e. this data is not available from the specified source. 

A-147 
 

 

 

 

Table A- 119: 2008 Data and CH4 Emissions (Mg) for the Natural Gas Processing Stage 

2008 EPA Adjusted Values 

Activity Activity Data Emission Factor Emissions 

Plants

Recip. Compressors 

Centrifugal Compressors 

Compressor Exhaust 

 Gas Engines 

 Gas Turbines 

AGR Vents 

Kimray Pumps 

Dehydrator Vents 

Pneumatic Devices 

Blowdowns/Venting 

577 

4,781 

771 

34,346 

40,725 

292 

1,244,246 

11,209,420 

577 

577 

plants 

compressors 

compressors 

MMHPhr 

MMHPhr 

AGR units 

MMscf/yr 

MMscf/yr 

gas plants 

gas plants 

7,906 

11,196 

21,230 

0.2 

0.01 

6,083 

178 

122 

164,721 

4,060 

scfd/plant 

scfd/comp 

scfd/comp 

scf/HPhr 

scf/HPhr 

scfd/AGR 

scf/MMscf 

scf/MMscf 

scfy/plant 

Mscfy/plant 

32,069 

376,275 

114,997 

158,762

4,471 

12,506 

4,260 

26,242 

1,831 

45,119 

Table A- 120: 2008 Data and CH4 Emissions (Mg) for the Natural Gas Transmission Stage 

Activity

2008 EPA Adjusted Values 

 Activity Data Emission Factor Emissions 

Pipeline Leaks 

Compressor Stations (Transmission) 

Station

Recip Compressor 

Centrifugal Compressor 

Compressor Stations (Storage) 

Station

Recip Compressor 

Centrifugal Compressor 

Wells (Storage) 

M&R (Trans. Co. Interconnect) 

M& R (Farm Taps + Direct Sales) 

Dehydrator vents (Transmission) 

Dehydrator vents (Storage) 

Compressor Exhaust 

Engines (Transmission) 

Turbines (Transmission) 

Engines (Storage) 

Turbines (Storage) 

Generators (Engines) 

Generators (Turbines) 

Pneumatic Devices Trans + Stor 

Pneumatic Devices Trans 

Pneumatic Devices Storage 

Routine Maintenance/Upsets 

Pipeline venting 

Station Venting Trans + Storage 

Station Venting Transmission 

Station Venting Storage 

LNG Storage 

LNG Stations 

LNG Reciprocating Compressors 

LNG Centrifugal Compressors 

LNG Compressor Exhaust 

LNG Engines 

LNG Turbines 

LNG Station Venting 

LNG Import Terminals 

LNG Stations 

LNG Reciprocating Compressors 

LNG Centrifugal Compressors 

LNG Compressor Exhaust 

LNG Engines 

294,488 miles 2 Scfd/ mile 

1,748 Stations 8,778 Scfd/station 

7,028 Compressors 15,205 Scfd/ comp 

705 Compressors 30,305 Scfd/ comp 

400 Stations 21,507 Scfd/ comp 

1,178 Compressors 21,116 Scfd/ comp 

116 Compressors 30,573 Scfd/ comp 

18,673 Stations 115 Scfd/ comp 

2,621 Stations 3,984 scfd/station 

77,729 Stations 31 scfd/station 

1,114,305 MMscf/Year 94 scf/MMscf 

2,074,894 MMscf/Year 117 scf/MMscf 

46,332 MMHPhr 0.2 scf/HPhr 

11,055 MMHPhr 0.01 scf/HPhr 

5,106 MMHPhr 0.2 scf/HPhr 

1,794 MMHPhr 0 scf/HPhr 

2,267 MMHPhr 0 scf/HPhr 

27 MMHPhr 0 scf/HPhr 

68,809 Devices 162,197 Scfy/device 

15,763 Devices 162,197 Scfy/device 

294,488 Miles 32 Mscfy/mile 

1,748 Compressor 

Stations 4,359 Mscfy/station 

400 Compressor 

Stations 4,359 Mscfy/station 

70 Stations 21,507 scfd/station 

270 Compressors 21,116 scfd/comp 

64 Compressors 30,573 scfd/comp 

718 MMHPhr 0.2 scf/HPhr 

113 MMHPhr 0.01 scf/HPhr 

70 Stations 4,359 Mscfy/station 

7 Stations 21,507 scfd/station 

34 Compressors 21,116 scfd/comp 

6 Compressors 30,573 scfd/comp 

1,496 MMHPhr 0.2 scf/HPhr 

3,217 

107,873 

751,258 

150,174 

60,546 

174,866 

24,931 

15,030 

73,420 

17,049 

2,011 

4,683 

214,167 

1,214 

23,603 

197 

10,480 

3 

214,952 

49,242 

179,514 

146,761 

33,620 

10,623 

40,147 

13,766 

3,320 

12 

5,899 

1,058 

5,047 

1,290 

6,913 

A-148 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2008 
 

LNG Turbines 358 MMHPhr 0.01 scf/HPhr 39 

LNG Station Venting 7 Stations 4,359 Mscfy/station 588 

Table A- 121: 2008 Data and CH4 Emissions (Mg) for the Natural Gas Distribution Stage 

Activity 

2008 EPA Adjusted Values 

Activity Data Emission Factor Emissions 

Pipeline Leaks 

Mains—Cast Iron 36,462 miles 239 Mscf/mile-yr 167,628 

Mains—Unprotected steel 69,374 miles 110 Mscf/mile-yr 147,229 

Mains—Protected steel 479,502 miles 3 Mscf/mile-yr 28,324 

Mains—Plastic 603,377 miles 10 Mscf/mile-yr 115,164 

Services—Unprotected steel 5,388,623 services 2 Mscf/service 176,514 

Services Protected steel 15,456,866 services 0.2 Mscf/service 52,543 

Services—Plastic 41,573,069 services 0.01 Mscf/service 7,445 

Services—Copper

Meter/Regulator (City Gates) 

 1,140,738 services 0.3 Mscf/service 5,588 

M&R >300 4,033 stations 180 scfh/station 122,342 

M&R 100-300 14,718 stations 96 scfh/station 237,389 

M&R <100 7,867 stations 4 scfh/station 5,720 

Reg >300 4,409 stations 162 scfh/station 120,441 

R-Vault >300 2,590 stations 1 scfh/station 568 

Reg 100-300 13,339 stations 41 scfh/station 91,145 

R-Vault 100-300 5,993 stations 0.2 scfh/station 182 

Reg 40-100 40,028 stations 1 scfh/station 7,024 

R-Vault 40-100 35,497 stations 0.1 scfh/station 518 

Reg <40 

Customer Meters 

16,973 stations 0.1 scfh/station 381 

Residential 41,549,008 outdr meters 143 scfy/meter 114,650 

Commercial/Industry 

Routine Maintenance 

4,345,918 meters 48 scfy/meter 4,009 

Pressure Relief Valve Releases 1,188,714 mile main 0.1 Mscf/mile 1,145 

Pipeline Blowdown 

Upsets 

1,346,158 miles 0.1 Mscfy/mile 2,645 

Mishaps (Dig-ins) 1,346,158 miles 2 mscfy/mile 41,224 

A-149 
Table A- 122: Key Activity Data Drivers 

Variable Units 1990 1995 2002 2003 2004 2005 2006 

Transmission Pipelines Length miles 291,990 296,947 303,541 301,827 303,095 300,542 300,321 

Wells 

NE—Associated Gas Wells* # wells 68,261 66,102 52,928 47,803 47,412 46,471 47,034 

NE—Non-associated Gas Wells* # wells 124,241 129,789 154,590 156,320 155,257 158,238 164,322 

MC—Associated Gas Wells* # wells 64,379 72,483 65,786 65,864 65,902 65,652 65,903 

MC—Non-associated Gas Wells* # wells 53,940 65,585 67,861 70,377 72,809 71,379 73,914 

RM—Associated Gas Wells* # wells 13,749 13,745 12,446 12,495 12,723 13,259 13,437 

RM—Non-associated Gas Wells* # wells 24,339 32,668 72,438 71,239 70,770 72,579 75,170 

SW—Associated Gas Wells* # wells 69,339 59,954 60,623 60,315 59,381 54,781 54,550 

SW—Non-associated Gas Wells* # wells 24,217 27,392 35,025 36,648 37,219 34,247 35,417 

WC—Associated Gas Wells* # wells 20,672 19,109 22,503 22,263 22,584 21,562 22,189 

WC—Non-associated Gas Wells* # wells 1,292 1,114 1,415 1,459 1,388 1,424 1,503 

GC—Associated Gas Wells* # wells 36,279 34,792 29,880 28,078 27,675 28,090 27,319 

GC—Non-associated Gas Wells* # wells 41,753 

Platforms 

Gulf of Mexico and Pacific OCS Off-shore 

41,978 53,198 54,245 54,544 57,600 60,715 

Platforms # platforms 3,941 

GoM and Pacific OCS Deep Water 

3,978 4051 4003 3932 3908 3912 

Platforms # platforms 17 23 44 46 50 59 67 

Gas Plants # gas plants 761 675 590 574 572 566 571 

Distribution Services # of services 47,883,083 54,644,033 58,876,416 58,537,395 61,089,889 58,556,335 62,255,435 

Steel—Unprotected # of services 7,633,526 6,151,653 5,186,134 4,840,347 4,791,652 5,308,375 5,642,470 

Steel—Protected # of services 19,781,581 21,002,455 17,778,463 17,258,710 18,147,587 15,883,423 15,732,037 

Plastic # of services 18,879,865 26,044,545 34,547,274 35,071,961 36,811,107 36,152,277 39,632,313 

Copper # of services 1,588,111 1,445,380 1,364,545 1,366,377 1,339,543 1,212,260 1,248,615 

Distribution Mains miles 944,157 1,001,706 1,133,625 1,104,683 1,151,995 1,093,909 1,209,419 

Cast Iron miles 58,292 50,625 42,025 41,091 40,600 37,371 36,977 

Steel—Unprotected miles 108,941 94,058 78,119 74,042 75,859 69,291 71,738 

Steel—Protected miles 465,538 503,288 480,982 483,782 495,861 461,459 481,811 

Plastic miles 311,386 353,735 532,499 505,768 539,675 525,788 618,893 

* NEMS (National Energy Modeling System) projects the production, imports, conversion, consumption, and prices of energy, subject to assumptions on macroeconomic and financial factors, world encosts, behavioral and technological choice criteria, cost and performance characteristics of energy technologies, and demographics 

A-150 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2008 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table A- 123: CH4 Reductions Derived from the Natural Gas STAR Program (Gg) 

Process 1992* 1995 2002 2003 2004 2005 2006 2007 2008 

Production - 75 439 615 1,002 1,425 1,469 1,857 2,227 

Processing - 5 38 68 65 129 140 139 145 

Transmission and Storage - 121 344 330 416 512 505 487 471 

Distribution - 19 151 116 100 35 48 34 26 

Total - 220 972 1,130 1,583 2,101 2,162 2,518 2,869 

*Reductions are relative to 1992; therefore, there are zero reductionsin 1992. 

Note: These reductions will not match the Natural Gas STAR program reductions. These numbers are adjusted for reductions prior to the 1992 base year, and do not 

include a sunsetting period. Totals may not sum due to independent rounding.
 

Table A- 124: CH4 Reductions Derived from NESHAP Regulations (Gg) 

Process 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 

Production 24.0 25.4 27.6 28.6 28.6 28.4 28.9 30.5 31.6 32.8 

Processing 

Transmission and Storage 

Distribution

12.7 

NA 

NA 

12.9

NA 

NA 

13.2 

NA 

NA 

12.7 

NA 

NA 

12.8

NA 

NA 

12.5

NA 

NA 

12.1 

NA 

NA 

12.4 

NA 

NA 

12.9 

NA 

NA 

13.9 

NA 

NA 

Total 36.7 38.3 40.8 41.3 41.4 40.9 41.0 43.0 44.5 46.7 

NA Not applicable 

Note: NESHAP regulations went into effect in 1999. Totals may not sum due to independent rounding.
 

Table A- 125: CH4 Emission Estimates from the Natural Gas Production Stage Exluding Reductions from the Natural Gas 

STAR Program and NESHAP regulations (Gg) 

Activity 1990 1992 

Normal Fugitives

 Gas Wells 

Non-Associated Gas Wells (less 

conventional)

 Unconventional Gas Wells 

 Field Separation Equipment

 Heaters 

 Separators 

 Dehydrators 

 Meter/ Piping
 

 Gathering Compressors

 Small Reciprocating Comp. 

 Large Reciprocating Comp. 

 Large Reciprocating Stations 

 Pipeline Leaks 

Vented and Combusted 

 Drilling and Well Completion

 Completion Flaring 

 Well Drilling 

 Coal Bed Methane 

 Powder River 

 Black Warrior 

 Normal Operations

 Pneumatic Device Vents 

 Chemical Injection Pumps 

 Kimray Pumps 

 Dehydrator Vents 

 Condensate Tank Vents

 Condensate Tanks without 

Control Device 

 Condensate Tanks with Control 

Device 

 Compressor Exhaust Vented

 Gas Engines 

 Well Workovers

 Gas Wells 

Well Clean Ups (LP Gas Wells) 

 Blowdowns 

30.82

0.01

12.57

43.83

14.75

43.61

30.22

7.50

0.51

98.03

0.01 

0.74

0.04

2.72

569.76

26.89

131.82

41.10

23.59

4.72 

119.06

0.56 

106.80

 31.68 

0.02 

13.28 

44.16 

15.76 

44.95 

32.15 

8.56 

0.58 

 102.22 

0.01 

0.54 

0.47 

4.84 

 607.88 

29.38 

 140.65 

43.86 

21.69 

4.34 

 125.48 

0.58 

 111.49 

1995 2002 2003 2004 2005 2006 2007 2008 

37.42 

0.04 

16.48 

54.79 

17.89 

54.89 

38.27 

9.80 

0.66 

114.49 

0.01 

0.53 

1.48 

6.25 

697.61 

35.04 

159.45 

49.72 

20.22 

4.04 

151.43 

0.64 

122.33 

51.07 50.29 50.09 49.40 50.87 52.01 56.05

0.67 0.85 0.98 1.21 1.33 1.52 1.70

26.44 26.60 26.67 26.94 28.00 28.44 32.05

84.15 85.03 85.25 86.52 90.23 94.19 102.77

23.28 23.62 23.73 23.96 24.90 26.20 27.55

81.96 82.73 83.08 83.81 87.15 90.37 98.98

52.53 53.52 53.99 53.89 56.03 58.55 63.46

12.62 12.48 12.61 12.60 12.58 12.56 13.41

0.86 0.85 0.86 0.85 0.85 0.85 0.91

145.52 145.56 147.60 148.53 152.90 158.22 167.21 

0.01 0.01 0.01 0.01 0.01 0.01 0.01

1.01 1.17 1.37 1.61 1.88 2.00 2.04

47.17 46.85 44.74 46.37 56.55 54.12 57.04

7.81 8.54 9.22 9.88 10.45 11.08 11.69

932.14 937.52 955.82 955.56 990.34 1,031.91 1,109.25

49.42 51.28 51.80 51.93 53.85 54.98 61.45

207.39 210.19 211.38 213.42 221.79 233.31 245.35

64.67 65.54 65.91 66.55 69.16 72.75 76.50

24.43 23.59 22.54 23.59 25.90 25.69 25.69

4.89 4.72 4.51 4.72 5.18 5.14 5.14

208.50 212.13 214.62 215.27 223.88 235.54 254.32

0.82 0.82 0.84 0.84 0.87 0.92 0.97 

157.67 156.89 160.77 162.03 167.93 176.14 185.57

A-151 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 Vessel BD
 

 Pipeline BD
 

 Compressor BD
 

 Compressor Starts 

Upsets 

 Pressure Relief Valves
 

Mishaps
 

Offshore

 Offshore water Gas Platforms 

(GoM & Pacific) 

 Deepwater Gas Platforms (GoM & 

Pacific) 

0.36 

1.56

1.17

2.61

0.34

0.85

290.49

5.21 

Total 1,612 1,696

0.38 

1.63 

1.24 

2.78 

0.35 

0.88 

 297.77 

5.94 

0.42 

1.82 

1.48 

3.31 

0.39 

0.99 

307.32 

7.40 

0.55 0.55 0.56 0.56 0.58

2.32 2.32 2.35 2.37 2.44

2.03 2.07 2.08 2.08 2.16

4.54 4.62 4.66 4.66 4.84

0.50 0.50 0.51 0.51 0.53

1.25 1.25 1.27 1.28 1.32

331.99 330.76 324.49 321.73 321.34

15.10 15.93 17.31 20.43 23.20

 0.61 0.65

 2.52 2.66

 2.26 2.45

 5.06 5.48

 0.56 0.59

 1.36 1.44 

 305.09 299.06

 21.10 21.78 

1,917 2,543 2,559 2,582 2,593 2,689 2,765 2,933 

Note: Totals may not sum due to independent rounding. 

Table A- 126: CH4 Emission Estimates from the Natural Gas Processing Plants Exluding Reductions from the Natural Gas 

STAR Program and NESHAP regulations (Gg) 

Activity 1990 1992 1995 2002 2003 2004 2005 2006 2007 2008 

Normal Fugitives 

Plants 42.30 40.68 37.52 32.79 31.90 31.79 31.46 31.74 31.90 32.07

 Reciprocating 

Compressors 324.94 324.74 338.42 344.69 347.39 338.24 327.87 337.12 348.25 376.28

 Centrifugal Compressors 99.31 99.25 103.43 105.34 106.17 103.37 100.20 103.03 106.43 115.00 

Vented and Combusted 

 Normal Operations 

 Compressor Exhaust 

 Gas Engines 137.10 137.02 142.79 145.43 146.57 142.71 138.34 142.24 146.94 158.76

 Gas Turbines 3.86 3.86 4.02 4.10 4.13 4.02 3.90 4.01 4.14 4.47 

AGR Vents 16.49 15.87 14.63 12.79 12.44 12.40 12.27 12.38 12.44 12.51

 Kimray Pumps 3.68 3.68 3.83 3.90 3.93 3.83 3.71 3.82 3.94 4.26

 Dehydrator Vents 22.66 22.65 23.60 24.04 24.23 23.59 22.87 23.51 24.29 26.24

 Pneumatic Devices 2.41 2.32 2.14 1.87 1.82 1.81 1.80 1.81 1.82 1.83 

Routine Maintenance 

 Blowdowns/Venting 59.51 57.24 52.78 46.14 44.88 44.73 44.26 44.65 44.88 45.12 

Total 712 707 723 721 723 706 687 704 725 777 

Note: Totals may not sum due to independent rounding. 

A-152 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2008
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table A- 127: CH4 Emission Estimates from the Natural Gas Transmission and Storage Exluding Reductions from the 

Natural Gas STAR Program and NESHAP regulations (Gg) 

Activity 1990 1992 1995 2002 2003 2004 2005 2006 2007 2008 

Fugitives 

 Pipelines Leaks 3.19 3.18 3.24 3.32 3.30 3.31 3.28 3.28 3.29 3.22 

Compressor Stations 

(Transmission)

 Station 106.96 106.77 108.77 111.19 110.56 111.03 110.09 110.01 110.26 107.87

 Recip Compressor 744.89 743.55 757.53 774.35 769.98 773.22 766.70 766.14 767.86 751.26

 Centrifugal Compressor 148.90 148.63 151.43 154.79 153.92 154.56 153.26 153.15 153.49 150.17 

Compressor Stations 

(Storage)

 Station 54.64 58.36 60.35 60.83 63.20 60.58 60.06 54.36 58.70 60.55

 Recip Compressor 157.80 168.48 174.27 175.76 182.59 175.01 173.53 157.05 169.52 174.87

 Centrifugal 

 Compressor 22.35 23.86 24.72 24.93 26.01 24.93 24.72 22.35 24.07 24.93

 Wells (Storage) 13.56 14.49 14.98 15.10 15.69 15.04 14.91 13.49 14.57 15.03

 M&R (Trans. Co. 

Interconnect) 72.80 72.67 74.03 75.68 75.25 75.57 74.93 74.87 75.04 73.42

 M&R (Farm Taps + Direct 

Sales) 16.90 16.87 17.19 17.57 17.47 17.55 17.40 17.39 17.43 17.05 

Vented and Combusted 

Normal Operation

 Dehydrator Vents 

(Transmission) 1.99 1.99 2.03 2.07 2.06 2.07 2.05 2.05 2.06 2.01 

Dehydrator Vents 

(Storage) 4.23 4.51 4.67 4.71 4.89 4.69 4.65 4.20 4.54 4.68 

Compressor Exhaust 

Engines (Transmission) 176.92 186.65 204.91 212.29 205.55 206.59 203.10 200.09 212.66 214.17 

Turbines (Transmission) 1.00 1.06 1.16 1.20 1.16 1.17 1.15 1.13 1.21 1.21 

Engines (Storage) 21.30 22.75 23.53 23.72 24.64 23.62 23.41 21.19 22.88 23.60 

Turbines (Storage) 0.18 0.19 0.20 0.20 0.21 0.20 0.20 0.18 0.19 0.20 

Generators (Engines) 8.66 9.13 10.03 10.39 10.06 10.11 9.94 9.79 10.41 10.48 

Generators (Turbines) 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 

Pneumatic Devices 

Trans+Stor 

Pneumatic Devices Trans 213.13 212.75 216.75 221.56 220.31 221.23 219.37 219.21 219.70 214.95 

Pneumatic Devices Storage 44.44 47.46 49.09 49.48 51.40 49.27 48.85 44.21 47.74 49.24 

Routine Maintenance/Upsets 

Pipeline Venting 177.99 177.67 181.01 185.03 183.99 184.76 183.20 183.07 183.48 179.51 

Station venting

Trans+Storage 

Station Venting 

Transmission 145.52 145.26 147.99 151.27 150.42 151.05 149.78 149.67 150.00 146.76 

Station Venting Storage 30.34 32.41 33.51 33.78 35.10 33.64 33.35 30.18 32.59 33.62 

LNG Storage 

LNG Stations 9.24 9.45 9.77 10.52 10.62 10.62 10.62 10.62 10.62 10.62 

LNG Reciprocating 

Compressors 34.50 35.37 36.67 39.71 40.15 40.15 40.15 40.15 40.15 40.15 

LNG Centrifugal 

Compressors 11.78 12.09 12.55 13.61 13.77 13.77 13.77 13.77 13.77 13.77 

LNG Compressor Exhaust 

LNG Engines 3.21 3.23 3.25 3.31 3.32 3.32 3.32 3.32 3.32 3.32 

LNG Turbines 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 

LNG Station Venting 5.13 5.25 5.43 5.84 5.90 5.90 5.90 5.90 5.90 5.90 

LNG Import Terminals 

LNG Stations 0.21 0.21 0.21 0.32 0.42 0.42 0.42 0.42 0.42 1.06 

LNG Reciprocating 

Compressors 1.01 1.01 1.01 1.51 2.02 2.02 2.02 2.02 2.02 5.05 

LNG Centrifugal 

Compressors 0.26 0.26 0.26 0.39 0.52 0.52 0.52 0.52 0.52 1.29 

LNG Compressor Exhaust 

LNG Engines 1.74 0.96 0.49 4.52 9.83 12.57 12.18 11.28 14.81 6.91 

LNG Turbines1 0.01 0.00 0.00 0.03 0.06 0.07 0.07 0.07 0.09 0.04 

A-153 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

LNG Station Venting 0.12 0.12 0.12 0.18 0.24 0.24 0.24 0.24 0.24 0.59 

Total 2,235 2,267 2,331 2,389 2,395 2,389 2,367 2,325 2,374 2,348 1 Emissions are not actually 0, but too small to show at this level of precision.

 Note: Totals may not sum due to independent rounding. 

Table A- 128: CH4 Emission Estimates from the Natural Gas Distribution Stage Exluding Reductions from the Natural Gas 

STAR Program (Gg) 

Activity 1990 1992 1995 2002 2003 2004 2005 2006 2007 2008 

Pipeline Leaks

 Mains—Cast Iron 267.99 243.28 232.74 193.20 188.91 186.65 171.81 170.00 173.18 167.63

 Mains—Unprotected steel 231.20 211.42 199.62 165.79 157.14 160.99 147.05 152.25 147.55 147.23

 Mains—Protected steel 27.50 27.71 29.73 28.41 28.58 29.29 27.26 28.46 28.93 28.32

 Mains—Plastic 59.43 51.02 67.52 101.64 96.53 103.01 100.36 118.13 114.82 115.16

 Services—Unprotected steel 250.05 233.84 201.51 169.88 158.55 156.96 173.89 184.83 178.49 176.51

 Services Protected steel 67.24 67.11 71.39 60.43 58.67 61.69 53.99 53.48 53.56 52.54

 Services—Plastic 3.38 3.71 4.66 6.19 6.28 6.59 6.47 7.10 7.36 7.44

 Services—Copper 7.78 7.68 7.08 6.68 6.69 6.56 5.94 6.12 6.01 5.59 

Meter/Regulator (City Gates)

 M&R >300 110.41 117.93 121.96 122.92 127.71 122.42 121.36 109.84 118.61 122.34

 M&R 100-300 214.25 228.82 236.64 238.52 247.81 237.54 235.49 213.13 230.15 237.39

 M&R <100 5.16 5.51 5.70 5.75 5.97 5.72 5.67 5.14 5.55 5.72

 Reg >300 108.70 116.09 120.06 121.01 125.73 120.52 119.48 108.13 116.77 120.44

 R-Vault >300 0.51 0.55 0.57 0.57 0.59 0.57 0.56 0.51 0.55 0.57

 Reg 100-300 82.26 87.86 90.86 91.58 95.15 91.20 90.42 81.83 88.37 91.15

 R-Vault 100-300 0.16 0.18 0.18 0.18 0.19 0.18 0.18 0.16 0.18 0.18

 Reg 40-100 6.34 6.77 7.00 7.06 7.33 7.03 6.97 6.31 6.81 7.02

 R-Vault 40-100 0.47 0.50 0.52 0.52 0.54 0.52 0.51 0.47 0.50 0.52

 Reg <40 0.34 0.37 0.38 0.38 0.40 0.38 0.38 0.34 0.37 0.38 

Customer Meters

 Residential 103.47 110.51 114.29 115.20 119.68 114.72 113.73 102.93 111.15 114.65

 Commercial/Industry 3.97 4.25 4.78 4.38 4.25 4.27 3.95 3.85 3.97 4.01 

Routine Maintenance

 Pressure Relief Valve Releases 0.91 0.86 0.96 1.09 1.06 1.11 1.05 1.16 1.15 1.14

 Pipeline Blowdown 2.39 2.55 2.64 2.66 2.76 2.65 2.62 2.37 2.56 2.64 

Upsets

Mishaps (Dig-ins) 37.20 39.74 41.09 41.42 43.03 41.25 40.89 37.01 39.97 41.22

Total 1,591 1,568 1,562 1,485 1,484 1,462 1,430 1,394 1,437 1,450 

Note: Totals may not sum due to independent rounding. 

Table A- 129: U.S. Production Sector CO2 Content in Natural Gas by NEMS Region and Natural Gas Well type

Well Types North East Mid-Central Gulf Coast 

 U.S. Region 

South West Rocky Mountain West Coast Lower-48 States 

Conventional 0.92% 0.79% 2.17% 3.81% 7.95% 0.16% 3.41% 

Un-conventional 7.42% 0.31% 0.23% NA 0.64% NA 4.83% 

All types 3.04% 0.79% 2.17% 3.81% 7.58% 0.16% 3.45% 

Table A- 130: CO2 Emission Estimates from the Natural Gas Production Stage (Gg) 

Activity 1990 1992 1995 2002 2003 2004 2005 2006 2007 2008 

Normal Fugitives 

 Gas Wells

 Associated Gas Wells 3.56 3.57 4.25 6.67 6.44 6.27 6.04 6.18 5.87 7.01 

 Unconventional Gas Wells2 0.00 0.00 0.00 0.01 0.02 0.02 0.03 0.03 0.03 0.03 

 Field Separation Equipment

 Heaters 1.86 1.91 2.32 4.42 4.39 4.38 4.44 4.61 4.48 5.35 

 Separators 6.04 5.97 7.17 12.55 12.56 12.56 12.70 13.20 13.16 15.21 

 Dehydrators 1.50 1.54 1.73 2.81 2.81 2.79 2.83 2.94 2.93 3.30 

 Meter/ Piping 5.85 5.85 6.95 12.12 12.12 12.11 12.23 12.69 12.57 14.61 

 Gathering Compressors

 Small Reciprocating Comp. 2.95 2.98 3.57 6.13 6.15 6.16 6.18 6.41 6.38 7.38 

 Large Reciprocating Comp. 0.69 0.91 1.02 1.40 1.40 1.40 1.40 1.40 1.40 1.62 

 Large Reciprocating Stations 0.05 0.06 0.07 0.09 0.09 0.09 0.09 0.09 0.09 0.11 

 Pipeline Leaks 10.75 10.85 11.99 17 18 17 18 18 18 20 

Vented and Combusted 

A-154 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2008 
 

 

 

 

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 Completion Flaring2 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 

Well Drilling	 0.07 0.05 0.05 0.11 0.13 0.15 0.18 0. 21 0.22 0.23

 Coal Bed Methane 

 Powder River1 - ­ -

 Black Warrior1 - ­ -

 Normal Operations

 Pneumatic Device Vents 58.49 60.24 69.38 114 114 114 115 119 119 136 

 Chemical Injection Pumps 2.95 3.11 3.75 7.00 7.09 7.08 7.19 7.45 7.20 8.66 

 Kimray Pumps 13.41 13.71 15.43 24.94 24.93 24.78 25.18 26.12 26.05 29.32 

 Dehydrator Vents 4.18 4.28 4.81 7.78 7.77 7.73 7.85 8.15 8.12 9.14 

 Condensate Tank Vents

 Condensate Tanks without 

Control Device 10.25 9.43 8.79 10.62 10.25 9.79 10.25 11.26 11.17 11.17 

 Condensate Tanks with Control 

Device 2.05 1.89 1.76 2.12 2.05 1.96 2.05 2.25 2.23 2.23 

 Compressor Exhaust Vented

 Gas Engines1 - ­ -

 Well Workovers - ­ -

 Gas Wells 0.06 0.06 0.06 0.09 0.09 0.09 0.09 0.10 0.10 0.11 

 Well Clean Ups (LP Gas Wells) 10.64 10.89 12.02 17.86 17.95 17.92 18.15 18.84 19.13 21.11 

 Blowdowns

 Vessel BD 0.04 0.04 0.04 0.06 0.06 0.06 0.07 0.07 0.07 0.08 

 Pipeline BD 0.17 0.17 0.19 0.28 0.28 0.28 0.28 0.29 0.29 0.32 

 Compressor BD 0.11 0.12 0.14 0.24 0.24 0.24 0.24 0.25 0.25 0.28 

 Compressor Starts 0.25 0.26 0.31 0.53 0.53 0.53 0.53 0.55 0.55 0.64 

Upsets 

 Pressure Relief Valves 0.03 0.03 0.04 0.06 0.06 0.06 0.06 0.06 0.06 0.07 

Mishaps 0.09 0.09 0.10 0.15 0.15 0.15 0.15 0.16 0.16 0.17 

 Flaring Emissions - Onshore 9,093 10,172 17,168 6,001 5,936 5,828 7,200 7,812 9,104 7,838 

Offshore 

Offshore water Gas Platforms (GoM 

& Pacific) 1.47 1.51 1.56 1.69 1.68 1.65 1.63 1.63 1.55 1.52 

Deepwater Gas Platforms (GoM & 

Pacific) 0.03 0.03 0.04 0.08 0.08 0.09 0.10 0.12 0.11 0.11 

 Flaring Emissions - Offshore 230 163 197 211 155 165 181 146 160 361 

Total 9,461 10,475 17,523 6,463 6,343 6,243 7,633 8,221 9,525 8,495 1 Energy use CO2 emissions not estimated to avoid double counting. 2	 Emissions are not actually 0, but too small to show at this level of precision. 

 Note: Totals may not sum due to independent rounding. 

Table A- 131: CO2 Emission Estimates from the Natural Gas Processing Plants (Gg) 

Activity 1990 1992 1995 2002 2003 2004 2005 2006 2007 2008 

Normal Fugitives 

Plants – Before CO2 removal 2.56 2.46 2.27 1.98 1.93 1.92 1.90 1.92 1.93 1.94 

Plants – After CO2 removal 0.57 0.55 0.50 0.44 0.43 0.43 0.42 0.43 0.43 0.43 

 Reciprocating Compressors –
 

Before CO2 removal 19.67 19.66 20.45 20.86 21.03 20.47 19.85 20.41 21.08 22.78 

 Reciprocating Compressors –
 

After CO2 removal 4.37 4.36 4.55 4.63 4.67 4.55 4.41 4.53 4.68 5.06 

 Centrifugal Compressors –
 

Before CO2 removal 6.01 6.01 6.26 6.38 6.43 6.26 6.07 6.24 6.44 6.96 

 Centrifugal Compressors –
 

After CO2 removal 1.33 1.33 1.39 1.42 1.43 1.39 1.35 1.38 1.43 1.55 

Vented and Combusted

 Normal Operations 

 Compressor Exhaust 

 Gas Engines1 - - -

Gas Turbines1 - ­ -

AGR Vents 27,708 26,652 24,577 23,022 21,958 21,737 21,694 21,161 21,144 21,328 

 Kimray Pumps 0.39 0.39 0.41 0.42 0.42 0.41 0.40 0.41 0.42 0.46 

 Dehydrator Vents 2.42 2.42 2.52 2.57 2.59 2.52 2.45 2.51 2.60 2.81 

 Pneumatic Devices 0.29 0.27 0.25 0.22 0.22 0.21 0.21 0.21 0.22 0.22 

Routine Maintenance 

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 Blowdowns/Venting 6.36 6.12 5.64 4.93 4.80 4.78 4.73 4.78 4.80 4.83 

Total 27,752 26,696 24,621 23,066 22,002 21,779 21,736 21,204 21,188 21,375 1 Energy use CO2 emissions not estimated to avoid double counting. 

Note: Totals may not sum due to independent rounding. 

Table A- 132: CO2 Emission Estimates from the Natural Gas Transmission and Storage (Gg) 

Activity 1990 1992 1995 2002 2003 2004 2005 2006 2007 2008 

Fugitives 

 Pipelines Leaks 0.09 0.09 0.09 0.10 0.10 0.10 0.09 0.09 0.09 0.09 

 Compressor Stations (Transmission)

 Station 3.09 3.08 3.14 3.21 3.19 3.20 3.18 3.17 3.18 3.11 

 Recip Compressor 21.49 21.45 21.85 22.34 22.21 22.30 22.12 22.10 22.15 21.67 

 Centrifugal Compressor 4.30 4.29 4.37 4.47 4.44 4.46 4.42 4.42 4.43 4.33 

 Compressor Stations (Storage)

 Station 1.58 1.68 1.74 1.75 1.82 1.75 1.73 1.57 1.69 1.75 

 Recip Compressor 4.55 4.86 5.03 5.07 5.27 5.05 5.01 4.53 4.89 5.04 

 Centrifugal Compressor 0.64 0.69 0.71 0.72 0.75 0.72 0.71 0.64 0.69 0.72 

 Wells (Storage) 0.39 0.42 0.43 0.44 0.45 0.43 0.43 0.39 0.42 0.43 

 M&R (Trans. Co. Interconnect) 2.10 2.10 2.14 2.18 2.17 2.18 2.16 2.16 2.16 2.12 

 M&R (Farm Taps + Direct Sales) 0.49 0.49 0.50 0.51 0.50 0.51 0.50 0.50 0.50 0.49 

Vented and Combusted

 Normal Operation 

 Dehydrator Vents (Transmission) 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 .06

 Dehydrator Vents (Storage) 0.12 0.13 0.13 0.14 0.14 0.14 0.13 0.12 0.13 .14

 Compressor Exhaust

 Engines (Transmission)1 - - -

 Turbines (Transmission)1 - - -

 Engines (Storage)1 - - -

 Turbines (Storage)1 - - -

 Generators (Engines)1 - - -

 Generators (Turbines)1 - - -

 Pneumatic Devices Trans+Stor

 Pneumatic Devices Trans 6.15 6.14 6.25 6.39 6.35 6.38 6.33 6.32 6.34 6.20

 Pneumatic Devices Storage 1.28 1.37 1.42 1.43 1.48 1.42 1.41 1.28 1.38 1.42 

 Routine Maintenance/Upsets 

 Pipeline Venting 5.13 5.13 5.22 5.34 5.31 5.33 5.28 5.28 5.29 5.18 

 Station venting Trans+Storage

 Station Venting Transmission 4.20 4.19 4.27 4.36 4.34 4.36 4.32 4.32 4.33 4.23 

 Station Venting Storage 0.88 0.93 0.97 0.97 1.01 0.97 0.96 0.87 0.94 0.97 

LNG Storage 

LNG Stations 0.31 0.32 0.33 0.35 0.36 0.36 0.36 0.36 0.36 0.36 

 LNG Reciprocating Compressors 1.16 1.18 1.23 1.33 1.34 1.34 1.34 1.34 1.34 1.34 

 LNG Centrifugal Compressors 0.39 0.41 0.42 0.46 0.46 0.46 0.46 0.46 0.46 0.46 

 LNG Compressor Exhaust 

 LNG Engines1 - - -

 LNG Turbines1 - - -

 LNG Station Venting 0.17 0.18 0.18 0.20 0.20 0.20 0.20 0.20 0.20 0.20 

LNG Import Terminals 

LNG Stations 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.04 

 LNG Reciprocating Compressors 0.03 0.03 0.03 0.05 0.07 0.07 0.07 0.07 0.07 0.17 

 LNG Centrifugal Compressors 0.01 0.01 0.01 0.01 0.02 0.02 0.02 0.02 0.02 0.04 

 LNG Compressor Exhaust 

 LNG Engines1 - - -

 LNG Turbines1 - - -

 LNG Station Venting2 0.00 0.00 0.00 0.01 0.01 0.01 0.01 0.01 0.01 0.02 

Total 59 59 61 62 62 62 61 60 61 61 1 Energy use CO2 emissions not estimated to avoid double counting. 2

 Emissions are not actually 0, but too small to show at this level of precision.

 Note: Totals may not sum due to independent rounding. 

Table A- 133: CO2 Emission Estimates from the Natural Gas Distribution Stage (Gg) 

Activity 1990 1992 1995 2002 2003 2004 2005 2006 2007 2008 

Pipeline Leaks

 Mains—Cast Iron 7.73 7.02 6.71 5.57 5.45 5.38 4.96 4.90 5.00 4.84 

 Mains—Unprotected steel 6.67 6.10 5.76 4.78 4.53 4.64 4.24 4.39 4.26 4.25 

A-156 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2008
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 Mains—Protected steel 0.79 0.80 0.86 0.82 0.82 0.84 0.79 0.82 0.83 0.82 

Mains—Plastic 1.71 1.47 1.95 2.93 2.78 2.97 2.89 3.41 3.31 3.32 

Total Pipeline Miles 

6.75 5.81 4.90 4.57 4.53 5.02 5.33 5.15 5.09 

 Services Protected steel 1.94 

 Services—Unprotected steel 7.21 

1.94 2.06 1.74 1.69 1.78 1.56 1.54 1.54 1.52

 Services—Plastic 0.10 0.11 0.13 0.18 0.18 0.19 0.19 0.20 0.21 0.21 

 Services—Copper 0.22 0.22 0.20 0.19 0.19 0.19 0.17 0.18 0.17 0.16 

Meter/Regulator (City Gates)

 M&R >300 3.18 3.40 3.52 3.55 3.68 3.53 3.50 3.17 3.42 3.53 

 M&R 100-300 6.18 6.60 6.83 6.88 7.15 6.85 6.79 6.15 6.64 6.85 

 M&R <100 0.15 0.16 0.16 0.17 0.17 0.17 0.16 0.15 0.16 0.17 

Reg >300 3.14 3.35 3.46 3.49 3.63 3.48 3.45 3.12 3.37 3.47 

 R-Vault >300 0.01 0.02 0.02 0.02 0.02 0.02 0.02 0.01 0.02 0.02 

 Reg 100-300 2.37 2.53 2.62 2.64 2.74 2.63 2.61 2.36 2.55 2.63 

 R-Vault 100-3001 0.00 0.01 0.01 0.01 0.01 0.01 0.01 0.00 0.01 0.01 

 Reg 40-100 0.18 0.20 0.20 0.20 0.21 0.20 0.20 0.18 0.20 0.20 

 R-Vault 40-100 0.01 0.01 0.01 0.02 0.02 0.01 0.01 0.01 0.01 0.01 

Reg <40 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 

Customer Meters

 3.19 3.30 3.32 3.45 3.31 3.28 2.97 3.21 3.31 

Commercial/Industry 0.11 

Residential 2.98 

0.12 0.14 0.13 0.12 0.12 0.11 0.11 0.11 0.12 

Routine Maintenance

 Pressure Relief Valve Releases 0.03 0.02 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 

 Pipeline Blowdown 0.07 0.07 0.08 0.08 0.08 0.08 0.08 0.07 0.07 0.08 

Upsets

 Mishaps (Dig-ins) 1.07 1.15 1.19 1.19 1.24 1.19 1.18 1.07 1.15 1.19 

Total 46 45 45 43 43 42 41 40 41 42 1 Emissions are not actually 0, but too small to show at this level of precision.

 Note: Totals may not sum due to independent rounding. 

A-157