U.S. Energy Information Administration www.eia.gov

AEO2018 Review & AEO2019 Plans

For

AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group

May 30, 2018 | Washington, D.C.

By

James Preciado, Liquid Fuels Markets Team

Dana Van Wagener, Exploration and Production Team

WORKING GROUP PRESENTATION FOR DISCUSSION PURPOSES

DO NOT QUOTE OR CITE AS RESULTS ARE SUBJECT TO CHANGE
Liquid Fuels Markets

2 James Preciado/ AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes

Washington, DC, May 30, 2018 DO NOT QUOTE OR CITE as results ae subject to change
Outline

• Brief background of the Liquid Fuels Market Module (LFMM) and 

International Energy Module (IEM)

• Evaluation and discussion of results from AEO2018

• Improvements for AEO2019

3 James Preciado/ AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes

Washington, DC, May 30, 2018 DO NOT QUOTE OR CITE as results ae subject to change
Outline

• Brief background of the Liquid Fuels Market Module (LFMM) and 

International Energy Module (IEM)

• Evaluation and discussion of results from AEO2018

• Improvements for AEO2019

4 James Preciado/ AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes

Washington, DC, May 30, 2018 DO NOT QUOTE OR CITE as results ae subject to change
Background on Liquid Fuels Market Module (LFMM) and 

International Energy Module (IEM)

• LFMM is a linear program that projects petroleum product prices and 

sources of liquid fuels supply for meeting petroleum product demand. The 

sources of supply include crude oil refined into petroleum products, imports 

of petroleum products, and non-petroleum liquids such as biofuels, coal-toliquids, and gas-to-liquids.

• IEM is an economic model that simulates the interaction between U.S. and 

global petroleum markets. It uses assumptions of economic growth and 

expectations of future world crude oil and liquids production and 

consumption to compute Brent crude oil prices, provides a supply curve of 

world crude like liquids, and generates a worldwide oil supply/demand 

balance with regional detail. 

5 James Preciado/ AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes

Washington, DC, May 30, 2018 DO NOT QUOTE OR CITE as results ae subject to change
Outline

• Brief background of the Liquid Fuels Market Module (LFMM) and 

International Energy Module (IEM)

• Evaluation and discussion of results from AEO2018

• Improvements for AEO2019

6 James Preciado/ AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes

Washington, DC, May 30, 2018 DO NOT QUOTE OR CITE as results ae subject to change
Oil prices continue to rise in the reference case projection

7

0

50

100

150

200

250

2010 2020 2030 2040 2050

2017

history projections

$229

$52

$114

High Oil Price

Low Oil and Gas 

Resource/Technology

Reference case

High Oil and Gas 

Resource/Technology

Low Oil Price

North Sea Brent oil price

2017 dollars per barrel

James Preciado/ AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes 

Washington, DC, May 30, 2018 DO NOT QUOTE OR CITE as results ae subject to change

Source: U.S. Energy Information Administration, Annual Energy Outlook 2018 
The United States becomes a net exporter of crude oil, petroleum 

products, and natural gas liquids in 2029

8

-60

-40

-20

0

20

40

60

80

2000 2010 2020 2030 2040 2050

2017

history projections

Low Oil Price

Low Oil and Gas

Resource/Technology

Reference

High Oil Price

High Oil and Gas

Resource/Technology

net imports

net exports

Petroleum net imports as a percentage of product supplied

Percent

James Preciado/ AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes 

Washington, DC, May 30, 2018 DO NOT QUOTE OR CITE as results ae subject to change

Source: U.S. Energy Information Administration, Annual Energy Outlook 2018 
0

1

2

3

4

5

6

7

8

9

10

2010 2015 2020 2025 2030 2035 2040 2045 2050

Total U.S. crude oil imports Total U.S. heavy crude oil imports

Crude oil imports

Millions of barrels per day

James Preciado/ AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes 

Washington, DC, May 30, 2018 DO NOT QUOTE OR CITE as results ae subject to change

While total crude oil imports decline in the reference case, imports of 

heavy crude oil increase to balance the crude slate

Source: U.S. Energy Information Administration, Annual Energy Outlook 2018 Reference case 

9

2017

history projections
0

10

20

30

40

50

60

70

80

90

100

2000 2010 2020 2030 2040 2050

U.S. refinery utilization

Percent operable capacity

James Preciado/ AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes 

Washington, DC, May 30, 2018 DO NOT QUOTE OR CITE as results ae subject to change

Refinery utilization rises in 2020 in reaction to increased international 

demand for diesel, but returns to historical levels

Source: U.S. Energy Information Administration, Annual Energy Outlook 2018

10

2017

history projections

Reference 

High Oil Price 

Low Oil Price 
0

50

100

150

200

250

300

350

400

450

2010 2020 2030 2040 2050

U.S. Imports of High Sulfur Resid

0

200

400

600

800

1,000

1,200

1,400

1,600

1,800

2,000

2010 2020 2030 2040 2050

U.S. Exports of ULSD

Imports

Thousands of b/d

Exports

Thousands of b/d

James Preciado/ AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes 

Washington, DC, May 30, 2018 DO NOT QUOTE OR CITE as results ae subject to change

Volumes of imports and exports of petroleum products shift as a result 

of the 2020 IMO regulation on sulfur content of marine fuel

Source: U.S. Energy Information Administration, Annual Energy Outlook 2018 Reference case

11

2017

history projections

2017

history projections
Outline

• Brief background of the Liquid Fuels Market Module (LFMM) and 

International Energy Module (IEM)

• Evaluation and discussion of results from AEO2018

• Improvements for AEO2019

12 James Preciado/ AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes 

Washington, DC, May 30, 2018 DO NOT QUOTE OR CITE as results ae subject to change
AEO2019 Planned improvements

13

• Update transportation costs between regions as well as import and exports 

costs for crude oil and petroleum products

• Assess the ability of the West Coast refineries to process additional volumes 

of Alaskan crude oil production

• Further analyze the effects of IMO regulations on sulfur content for marine 

gasoil starting in 2020 on international crude oil and product markets

• Some “under the hood” process improvements for benchmarking to the 

STEO forecast

James Preciado/ AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes 

Washington, DC, May 30, 2018 DO NOT QUOTE OR CITE as results ae subject to change
Oil and Gas Supply

14 Dana Van Wagener/ AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes 

Washington, DC, May 30, 2018 DO NOT QUOTE OR CITE as results ae subject to change
Outline

• Evaluation and discussion of results from AEO2018

• Review of changes to the short-term outlook

• Current plans for AEO2019

15 Dana Van Wagener/ AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes 

Washington, DC, May 30, 2018 DO NOT QUOTE OR CITE as results ae subject to change
Outline

• Evaluation and discussion of results from AEO2018

• Review of changes to the short-term outlook

• Current plans for AEO2019

16 Dana Van Wagener/ AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes 

Washington, DC, May 30, 2018 DO NOT QUOTE OR CITE as results ae subject to change
U.S. crude oil production

million barrels per day

U.S. dry natural gas production

trillion cubic feet billion cubic feet per day

U.S. crude oil and natural gas production continues to be driven by 

growth in tight oil and shale gas supply

17

0

2

4

6

8

10

12

14

2000 2010 2020 2030 2040 2050

other U.S.

tight oil

0

20

40

60

80

100

120

0

5

10

15

20

25

30

35

40

45

2000 2010 2020 2030 2040 2050

other U.S.

shale gas

2017

history projections

Note: Shale gas production includes associated natural gas from tight oil plays.

Source: U.S. Energy Information Administration, Annual Energy Outlook 2018 Reference case

Dana Van Wagener/ AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes 

Washington, DC, May 30, 2018 DO NOT QUOTE OR CITE as results ae subject to change

2017

history projections
Lower 48 onshore crude oil production by region

million barrels per day

Lower 48 onshore dry natural gas production by region

trillion cubic feet billion cubic feet per day

The Southwest region leads growth in U.S. crude oil production and 

the East region leads growth in natural gas in the Reference case

18

Source: U.S. Energy Information Administration, Annual Energy Outlook 2018 Reference case

0

1

2

3

4

5

2000 2010 2020 2030 2040 2050

2017

history projections

Southwest

Rocky Mountain/Dakotas 

Gulf Coast

Midcontinent

West Coast

East 0

10

20

30

40

50

60

0

5

10

15

20

25

2000 2010 2020 2030 2040 2050

2017

history projections

East

Gulf Coast

Southwest

Rocky Mountain/Dakotas 

Midcontinent

West Coast

Dana Van Wagener/ AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes 

Washington, DC, May 30, 2018 O NOT QUOTE OR CITE as results ae subject to change
0

1

2

3

4

2010 2015 2020 2025 2030 2035 2040 2045 2050

 Sum of selected Permian

 Wolfcamp*

 Bakken

 Other

 Eagle Ford

 Spraberry*

 Avalon/Bonespring*

 Austin Chalk

 Niobrara

 Woodford

 Monterey

U.S. tight oil production

million barrels per day

Bakken and Wolfcamp lead growth in tight oil production

*Permian Basin

Source: U.S. Energy Information Administration, Annual Energy Outlook 2018 Reference case

19

2017

history projections

Dana Van Wagener/ AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes 

Washington, DC, May 30, 2018 DO NOT QUOTE OR CITE as results ae subject to change
0

2

4

6

8

10

12

14

2010 2015 2020 2025 2030 2035 2040 2045 2050

 Marcellus

 Utica

 Other

 Haynesville/Bossier

 Eagle Ford

 Barnett

 Fayetteville

 Woodford

 Bakken

 Antrim

U.S. dry shale gas production

trillion cubic feet

Marcellus and Utica lead production of shale gas 

Note: Other includes natural gas production in tight oil plays.

Source: U.S. Energy Information Administration, Annual Energy Outlook 2018 Reference case

20

2017

history projections

Dana Van Wagener/ AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes 

Washington, DC, May 30, 2018 DO NOT QUOTE OR CITE as results ae subject to change
U.S. crude oil production

million barrels per day

U.S. dry natural gas production

trillion cubic feet per year billion cubic feet per day

U.S. crude oil and natural gas production are sensitive to resource 

availability and technological improvements

Source: U.S. Energy Information Administration, Annual Energy Outlook 2018

21

0

20

40

60

80

100

120

140

160

0

10

20

30

40

50

60

2000 2010 2020 2030 2040 2050

2017

history projections

Dana Van Wagener/ AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes 

Washington, DC, May 30, 2018 DO NOT QUOTE OR CITE as results ae subject to change

0

5

10

15

20

25

2010 2020 2030 2040 2050

2017

history projections

High Oil and Gas 

Resource and 

Technology 

High Oil Price

Reference case

Low Oil Price

Low Oil and Gas 

Resource and 

Technology
U.S. natural gas plant liquids production

million barrels per day

Natural gas plant liquids production increases from 2017 levels in all 

AEO2018 cases

Source: U.S. Energy Information Administration, Annual Energy Outlook 2018

22

0

1

2

3

4

5

6

7

8

2000 2010 2020 2030 2040 2050

2017

history projections

High Oil and Gas 

Resource and 

Technology

High Oil Price

High Economic 

Growth

Reference

Low Economic

Growth

Low Oil Price

Low Oil and Gas 

Resource and 

Technology

Dana Van Wagener/ AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes 

Washington, DC, May 30, 2018 DO NOT QUOTE OR CITE as results ae subject to change
0

1

2

3

4

5

6

7

2000 2010 2020 2030 2040 2050

2017

history projections

East

Southwest

Other U.S.

0

1

2

3

4

5

6

7

2000 2010 2020 2030 2040 2050

2017

history projections

natural gasoline

isobutane

normal butane

propane

ethane

U.S. natural gas plant liquids production by region

million barrels per day

U.S. natural gas plant liquids production by fuel

million barrels per day

The East and Southwest regions lead the production of natural gas 

plant liquids in the Reference case

Source: U.S. Energy Information Administration, Annual Energy Outlook 2018

23

Dana Van Wagener / AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes 

Washington, DC, May 30, 2018 DO NOT QUOTE OR CITE as results ae subject to change
0

50

100

150

200

250

2010 2020 2030 2040 2050

West Texas Intermediate oil price

2017 dollars per barrel

2017

history projections $224

$48

$110

0

2

4

6

8

10

2010 2020 2030 2040 2050

Henry Hub natural gas price

2017 dollars per million Btu

2017

history projections Low Oil and Gas 

Resource/Technology

High Oil Price

Reference case

Low Oil Price

High Oil and Gas 

Resource/Technology 

$9

$5

$3

Source: U.S. Energy Information Administration, Annual Energy Outlook 2018

Crude oil price projections are sensitive to global conditions, while U.S. 

natural gas prices depend more on domestic resource assumptions

24 Dana Van Wagener / AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes 

Washington, DC, May 30, 2018 DO NOT QUOTE OR CITE as results ae subject to change
Crude oil

(billion barrels)

Natural gas 

(trillion cubic feet)

Lower 48 onshore 194.1 1,907.1

East 4.6 707.1

Gulf Coast 37.8 423.9

Midcontinent 16.5 189.2

Southwest 80.9 238.7

Rocky Mountain/Dakotas 47.6 312.4

West Coast 6.6 35.8

Lower 48 offshore 54.4 279.6

Atlantic 3.3 31.7

Gulf of Mexico 44.6 238.3

Pacific 6.5 9.6

Alaska 36.1 275.6

Total U.S. 284.6 2,462.3

Resource 

Type

Drilling 

Cost

Lease 

Equipment 

& 

Operating 

Cost

EUR

Tier 1

EUR

Tier 2

EUR

Tier 2 

drilling 

ramp-up 

period

Tight oil -1.00% -0.50% 1.00% 3.00% 6.00%

Tight 

gas

-1.00% -0.50% 1.00% 3.00% 6.00%

Shale 

gas

-1.00% -0.50% 1.00% 3.00% 6.00%

All other -0.25% -0.25% 0.25% NA NA

EUR = estimated ultimate recovery

Technically recoverable resources (as of 1/1/2016) Annual average rate of technological improvement

Key oil and natural gas supply assumptions, AEO2018

25 Dana Van Wagener / AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes 

Washington, DC, May 30, 2018 DO NOT QUOTE OR CITE as results ae subject to change
Outline

• Evaluation and discussion of results from AEO2018

• Review of changes to the short-term outlook

• Current plans for AEO2019

26 Dana Van Wagener / AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes 

Washington, DC, May 30, 2018 DO NOT QUOTE OR CITE as results ae subject to change
West Texas Intermediate oil price

dollars per barrel 

West Texas Intermediate oil prices are forecast to average over 

$60/barrel in both 2018 & 2019 in the latest Short-Term Energy Outlook

Source: EIA Short-Term Energy Outlook, May 2018

27

0.00

20.00

40.00

60.00

80.00

100.00

120.00

2013 2014 2015 2016 2017 2018 2019

historical WTI spot price

STEO forecast

Nominal 

$/barrel AEO2018 May 2018 STEO

2017 $49.69 $50.79

2018 $50.57 $65.58

2019 $55.26 $60.86

Dana Van Wagener / AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes 

Washington, DC, May 30, 2018 DO NOT QUOTE OR CITE as results ae subject to change
0

2

4

6

8

10

12

14

2016 2017 2018 2019

-0.6

0.4

1.4 1.1

-1

0

1

2

2016 2017 2018 2019

Eagle Ford

Permian

Bakken

other

(net change)

U.S. crude oil production

million barrels per day

Components of annual change

million barrels per day

Higher prices drive crude oil production growth higher in the latest 

Short-Term Energy Outlook than in the AEO2018 Reference case

Source: EIA Short-Term Energy Outlook, May 2018 

28

history

STEO forecast

mmbd AEO2018 May 2018 STEO

2017 9.24 9.35

2018 9.95 10.72

2019 10.44 11.86

Dana Van Wagener / AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes 

Washington, DC, May 30, 2018 DO NOT QUOTE OR CITE as results ae subject to change
Henry Hub natural gas price

dollars per million British thermal units 

Henry Hub natural gas prices are forecast to average $3.01/MMBtu in 

2018 and $3.11/MMBtu in 2019 in the latest Short-Term Energy Outlook

Source: EIA Short-Term Energy Outlook, May 2018, and Thomson Reuters

29

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

2013 2014 2015 2016 2017 2018 2019

historical Henry Hub spot price

STEO forecast

Nominal 

$/MMBtu AEO2018 May 2018 STEO

2017 $3.05 $2.99

2018 $3.13 $3.01

2019 $3.55 $3.11

Dana Van Wagener / AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes 

Washington, DC, May 30, 2018 DO NOT QUOTE OR CITE as results ae subject to change
U.S. marketed natural gas production

billion cubic feet per day

Components of annual change

billion cubic feet per day

Marketed natural gas production is projected to grow by a record 7.4 

Bcf/d on average in 2018 in the latest Short-Term Energy Outlook

Source: EIA Short-Term Energy Outlook, May 2018 

30

0

10

20

30

40

50

60

70

80

90

100

2016 2017 2018 2019

historical marketed

production

-1.0

1.1

7.4

3.3

-5

-4

-3

-2

-1

0

1

2

3

4

5

6

7

8

9

2016 2017 2018 2019

Haynesville

Permian

Appalachia

other

(net change)

STEO forecast

Dana Van Wagener / AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes 

Washington, DC, May 30, 2018 DO NOT QUOTE OR CITE as results ae subject to change

bcf/d AEO2018

dry / marketed

May 2018 STEO 

dry / marketed

2017 74.2 / -- 73.6 / 78.9

2018 79.3 / -- 80.5 / 86.3

2019 85.5 / -- 83.3 / 89.6
Outline

• Evaluation and discussion of results from AEO2018

• Review of changes to the short-term outlook

• Current plans for AEO2019

31 Dana Van Wagener/ AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes 

Washington, DC, May 30, 2018 DO NOT QUOTE OR CITE as results ae subject to change
AEO2018 OGSM Lower 48 regions AEO2019 OGSM Lower 48 regions

Add Northern Great Plains region to AEO2019 published regional 

crude oil and natural gas supply tables

32 Dana Van Wagener/ AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes 

Washington, DC, May 30, 2018 DO NOT QUOTE OR CITE as results ae subject to change
• Currently there is only one form, or 

set of parameters, to define the short 

term supply curve for all OGSM 

districts (84)

• Code already includes optionality for 

up to 3 different forms of the supply 

curve, as well as fixed supply

• Allow for different supply elasticities 

for different types of regions

– Improve more granular results

– Allows different types of nonassociated 

supply (i.e. offshore, Marcellus, western 

Canada) to respond to price differently

Expand short-term supply curve options

33 Dana Van Wagener/ AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes 

Washington, DC, May 30, 2018 DO NOT QUOTE OR CITE as results ae subject to change
0

2

4

6

8

10

12

14

16

18

2010 2020 2030 2040 2050

2017

history projections Incremental production in High ANWR case

Incremental production in 

Mean ANWR case

Incremental production 

in Low ANWR case

U.S. crude oil production

million barrels per day

Include the coastal plain of the Arctic National Wildlife Refuge

34 Dana Van Wagener/ AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes 

Washington, DC, May 30, 2018 DO NOT QUOTE OR CITE as results ae subject to change

Source: U.S. Energy Information Administration, Annual Energy Outlook 2018
Other AEO2019 updates

• Tight oil and shale gas

– Estimated ultimate recovery

– Lateral length

– Well spacing

• NGPL assumptions for the DJ and Anadarko basins

• Lower 48 offshore and Alaska field declines and announced discoveries

• Current laws and regulations

35 Dana Van Wagener/ AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes 

Washington, DC, May 30, 2018 DO NOT QUOTE OR CITE as results ae subject to change
We welcome feedback on our assumptions and documentation

• Working group meetings http://www.eia.gov/forecasts/aeo/workinggroup/

• The AEO Assumptions report http://www.eia.gov/forecasts/aeo/assumptions/

• NEMS Model Documentation

– Oil and gas supply (OGSM) 

https://www.eia.gov/outlooks/aeo/nems/documentation/ogsm/pdf/m063(2017).pdf

– Liquid Fuels Market Module (LFMM) 

https://www.eia.gov/outlooks/aeo/nems/documentation/lfmm/pdf/m059(2014).pdf

– International Energy Module (IEM) 

https://www.eia.gov/outlooks/aeo/nems/documentation/international/pdf/m071(2016).pdf

• Working papers series http://www.eia.gov/workingpapers/

36 Dana Van Wagener/ AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes 

Washington, DC, May 30, 2018 DO NOT QUOTE OR CITE as results ae subject to change
For more information

U.S. Energy Information Administration home page | www.eia.gov

Annual Energy Outlook | www.eia.gov/aeo

Short-Term Energy Outlook | www.eia.gov/steo

International Energy Outlook | www.eia.gov/ieo

Monthly Energy Review | www.eia.gov/mer

Today in Energy | www.eia.gov/todayinenergy

State Energy Profiles | www.eia.gov/state

Drilling Productivity Report | www.eia.gov/petroleum/drilling/

International Energy Portal | www.eia.gov/beta/international/?src=home-b1

37 Dana Van Wagener/ AEO2019 Oil and Gas Supply & Liquid Fuels Markets Working Group Presentation for Discussion Purposes 

Washington, DC, May 30, 2018 DO NOT QUOTE OR CITE as results ae subject to change