Edgar Filing: Williams Partners L.P.

425

Filed by The Williams Companies, Inc.

Pursuant to Rule 425 under the Securities Act of 1933

Subject Company: Williams Partners L.P.

Commission File No.: 001-32599

The following is a slide presentation made available on the websites of The Williams Companies, Inc. and Williams Partners L.P. on September 2, 2014 in connection with a presentation at the 2014 Barclays Capital CEO Energy-Power Conference scheduled for September 3, 2014.

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Barclays CEO Energy-Power Conference

Alan Armstrong, Chief Executive Officer

September 3, 2014

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Important Information

This document does not constitute an offer to buy or solicitation of an offer to sell any securities. This document contains information related to a proposal which The Williams Companies, Inc. has made for a business combination transaction of Williams Partners L.P. (“WPZ”) and Access Midstream Partners, L.P. (“ACMP”). In furtherance of this proposal and subject to future developments, ACMP may file a registration statement with the SEC. INVESTORS ARE URGED TO READ THE REGISTRATION

STATEMENT, AND OTHER DOCUMENTS FILED WITH THE SEC CAREFULLY IN THEIR ENTIRETY IF AND WHEN THEY BECOME AVAILABLE AS THEY WILL CONTAIN IMPORTANT INFORMATION. Investors and security holders will be able to obtain free copies of these documents (if and when available) and other documents filed with the SEC by WPZ or ACMP through the website maintained by the SEC at http://www.sec.gov.

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Forward Looking Statements page 1 of 2

The reports, filings, and other public announcements of The Williams Companies, Inc. (Williams) and Williams Partners L.P. (WPZ) may contain or incorporate by reference statements that do not directly or exclusively relate to historical facts. Such statements are “forward-looking statements” within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended. We make these forward-looking statements in reliance on the safe harbor protections provided under the Private Securities Litigation Reform Act of 1995. You typically can identify forward-looking statements by various forms of words such as “anticipates,” “believes,” “seeks,” “could,” “may,” “should,” “continues,” “estimates,” “expects,” “forecasts,” “intends,” “might,” “proposed,” “goals,” “objectives,” “targets,” “planned,” “potential,” “projects,” “scheduled,” “will,” “assumes,” “guidance,” “outlook,” “in service date” or other similar expressions. These forward-looking statements are based on management’s beliefs and assumptions and on information currently available to management and include, among others, statements regarding:

The levels of dividends to Williams stockholders;

Expected levels of cash distributions by Access Midstream Partners, L.P. (“ACMP”) and WPZ with respect to general partner interests, incentive distribution rights, and limited partner interests;

Amounts and nature of future capital expenditures;

Expansion and growth of our business and operations;

Financial condition and liquidity;

Business strategy;

Cash flow from operations or results of operations;

Seasonality of certain business components

Natural gas, natural gas liquids, and olefins prices, supply, and demand; and

Demand for our service; and

The proposed merger of ACMP and WPZ (the Proposed Merger).

Forward-looking statements are based on numerous assumptions, uncertainties and risks that could cause future events or results to be materially different from those stated or implied in this presentation. Many of the factors that will determine these results are beyond our ability to control or predict. Specific factors that could cause actual results to differ from results contemplated by the forward-looking statements include, among others, the following:

Whether WPZ, ACMP, or the merged partnership will produce sufficient cash flows to provide the level of cash distributions we expect;

The structure, terms, timing and approval of the Proposed Merger, including as to be negotiated by the conflicts committees of ACMP and WPZ;

Whether Williams is able to pay current and expected levels of dividends;

Availability of supplies, market demand, and volatility of prices;

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Forward Looking Statements page 2 of 2

Inflation, interest rates, and fluctuation in foreign exchange rates and general economic conditions (including future disruptions and volatility in the global credit markets and the impact of these events on customers and suppliers);

The strength and financial resources of our competitors and the effects of competition;

Whether we are able to successfully identify, evaluate and execute investment opportunities;

Our ability to acquire new businesses and assets and successfully integrate those operations and assets, including ACMP’s business, into our existing businesses as well as successfully expand our facilities;

Development of alternative energy sources;

The impact of operational and developmental hazards and unforeseen interruptions;

The ability to recover expected insurance proceeds related to the Geismar plant;

Costs of, changes in, or the results of laws, government regulations (including safety and environmental regulations), environmental liabilities, litigation, and rate proceedings;

Williams’ costs and funding obligations for defined benefit pension plants and other postretirement benefit plans sponsored by its affiliates;

WPZ’s allocated costs for defined benefit pension plans and other postretirement benefit plans sponsored by its affiliates;

Changes in maintenance and construction costs;

Changes in the current geopolitical situation;

Exposure to the credit risk of our customers and counterparties;

Risks related to financing, including restrictions stemming from debt agreements, future changes in credit ratings and the availability and cost of capital;

The amount of cash distributions from and capital requirements of our investments and joint ventures in which we participate;

Risks associated with weather and natural phenomena, including climate conditions;

Acts of terrorism, including cybersecurity threats and related disruptions; and

Additional risks described in our filings with the Securities and Exchange Commission (SEC).

Given the uncertainties and risk factors that could cause our actual results to differ materially from those contained in any forward-looking statement, we caution investors not to unduly rely on our forward-looking statements. We disclaim any obligations to and do not intend to update the above list or announce publicly the result of any revisions to any of the forward-looking statements to reflect future events or developments.

In addition to causing our actual results to differ, the factors listed above may cause our intentions to change from those statements of intention set forth in this announcement. Such changes in our intentions may also cause our results to differ. We may change our intentions, at any time and without notice, based upon changes in such factors, our assumptions, or otherwise.

Investors are urged to closely consider the disclosures and risk factors in Williams’ and WPZ’s annual reports on Form 10-K filed with the SEC on Feb. 26, 2014, and each of our quarterly reports on Form 10-Q available from our offices or from our websites at www.williams.com and www.williamslp.com.

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Diverse, Large-Scale

Strategic Positions Delivering Value Today, Ongoing Growth

Marcellus-Utica Zoom-in View

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Williams’ Value Chain Adds Significant Growth

Foothold with ACMP Acquisition

Opportunities to extend services

ACMP

adds

>20% U.S. Dry-Gas Volumes Touch Our Systems

Transmission Pipelines and Storage

Market Hub

End User

Natural

Gas

Ethylene

Propylene

Mixed Multiple

Natural Gas Products

Wellhead Gas Gas Processing Liquids Fractionation Facilities Transmission Pipelines Olefins Plant End User

(onshore and Gathering Plants Storage Market Hub

offshore)

WPZ 11.0 Bcf/d 7 Bcf/d 418 231 Mbbl/d 22 MMbbl 386(lbs/year) 395MM lbs

inlet Mbbl/d Mbbl/d ethylene

ACMP 7.8 Bcf/d 1,900 MM storage

ethylene

815 MM 24 storage

475 Mbbl/d customers

crude oil propylene

7 exchange

partners

Figures represent 100% capacity for operated assets, including those in which Williams, WPZ and ACMP have a share of ownership;

NGL and derivatives storage includes capacity owned and under long-term lease; olefins-plant volumes are inclusive of Geismar, La.,

facility at full operation and expansion.

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We Are Well Positioned to Benefit

from Supply Growth

NATURAL GAS – U.S. SUPPLY GROWTH (Bcf/d)

Direct

CAGR CAGR Ownership

3% 3%

120

’09-’13 ’14-’30

+17% +58%

100 +9.5 +39.8 Bcf/d Northeast

Bcf/d Rockies

80 San Juan

Gulf of Mexico

60 Fort Worth

Mid-Continent

Gulf Coast

20 Permian

West Coast

0 Alaska

2000 2005 2010 2015 2020 2025 2030

Source: Wood Mackenzie North America Gas Service. Note: Excludes Canadian import volumes of approximately 4.5 Bcf/d (at 2014 levels).

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Demand Shows Up in Response to Supply, Price;

105 Bcf/d on

Conservative 2% CAGR

U.S. GAS DEMAND

(Bcf/d)

CAGR

2.5%

120

’09-’13

’14-’30

+14%

+47%

100

Other

+8.5

+33.5 Bcf/d

Transport

Bcf/d

LNG Exports

Power

40 Industrial

20 Commercial

Residential

2000 2003 2006 2009 2012 2015 2018 2021 2024 2027 2030

Source: Wood Mackenzie North America Gas Service

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Competitive Advantages Delivering Large-Scale Projects, Long-Term Value Creation

WEST ATLANTIC-GULF

> Increased fee-based revenues > Transco: Nation’s largest

to >80% of gross margins and fastest-growing pipeline

> Extensive network of large-scale assets, system with >50% capacity growth

well-positioned for NG supply growth in the next 4 years; connecting best

> Emerging demand growth in Pacific supplies to best markets

Northwest markets > Deepwater: Unique competitive

advantages driving strong revenue

> Prior large-scale investments still growth; executing on

generating high returns in low large-scale projects

NGL-margin environment

ACMP NGL & PETCHEM SERVICES

> Leadership positions in > Connecting upstream

nine unconventional supplies to new, growing

U.S. basins downstream customers

> Complementary position in > Bringing expanded

world’s largest shale play Geismar plant online

> Attractive return, > Growing unique Canadian

low-risk, fee-based business; Horizon, Syncrude,

business NE GATHERING & PROCESSING plus propane and proplyene

Expecting ~5 Bcf/d of capacity by 2015

Ideally situated in world’s largest shale play

Strong, growing free cash flows on the horizon

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Delivering Large-Scale Infrastructure to the

Marcellus & Utica

MARCELLUS & UTICA SHALE OVERVIEW Marcellus

(wholly owned or operated)

Susquehanna Supply Hub

(SSH) – 2015*

3 Bcf/d takeaway capacity

Laurel Mountain Midstream

(LMM) – 2015*

~700 MMcf/d gathering capacity

Ohio Valley Midstream (OVM) – 2015*

0.9 Bcf/d processing capacity

~80 Mbpd fractionation/de-ethanization

Access Midstream Partners – 2015*

3 Bcf/d estimated exit rate

Three Rivers Midstream (TRM)

248,000 dedicated acres

Utica

(partially owned, non-operated)

Blue Racer Midstream – 2015*

Bcf/d gathering capacity

Bcf/d processing capacity

~126 Mbpd fractionation capacity

Access Midstream Partners – 2015*

1 Bcf/d (operated) gathering exit rate

1.1 Bcf/d processing capacity

~135 Mbpd fractionation capacity

Represents estimated in-service dates and estimated capacity at respective year end.

LMM, Blue Racer and Access Midstream Partners Utica are partially owned systems; amounts shown reflect 100%.

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WPZ and ACMP: Large, Complementary Positions Serving the Best NE Marcellus Acreage

Gross Dedicated Acres

Laurel Mtn Midstream 500,000

ACMP – Marcellus 1,544,000

Ohio Valley Midstream 236,000

Susquehanna 150,000

Three Rivers JV 248,000

Total Marcellus 2,678,000

ACMP – Utica 1,631,000

Blue Racer JV—Utica >300,000

Total Utica >1,931,000

Total Marcellus + Utica >4,609,000

LMM, Blue Racer and Access Midstream Partners Utica are partially owned systems; amounts shown reflect 100%.

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WPZ and ACMP: Large, Complementary Positions Serving the Best SW Marcellus/Utica Acreage

LMM, Blue Racer and Access Midstream Partners Utica are partially owned systems; amounts shown reflect 100%.

Gross Dedicated Acres

Laurel Mtn Midstream 500,000

ACMP – Marcellus 1,544,000

Ohio Valley Midstream 236,000

Susquehanna 150,000

Three Rivers JV 248,000

Total Marcellus 2,678,000

ACMP – Utica 1,631,000

Blue Racer JV - Utica >300,000

Total Utica >1,931,000

Total Marcellus + Utica >4,609,000

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Transco: Nation’s Largest, Fastest Growing

Interstate Pipeline System

Garden State

NE Connector/

CAPITAL INVESTED PLACED Expansion Rockaway Lateral

INTO SERVICE ($B)

Leidy Atlantic

$4.8 Southeast Sunrise

2017

Constitution CPV

Woodbridge

Virginia Rock Springs

Southside Expansion

$1.6 2016 Hillabee Dalton Lateral

$1.3 2015 Phase 1

Mobile Bay

$0.3 2014 South III

Gulf Trace

Dates reflect expected in-service dates. The estimated project in-service dates assume timely receipt of all regulatory approvals.

Constitution expected in service late 2015 to 2016.

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Gas Pipeline Assets: Unprecedented Growth

with Fully Contracted Projects

CAPITAL INVESTMENT PLACED INTO SERVICE

($MM) MMdt/d

$4,000 16.5 18

2011-2014

$3,500

16 13 major

$3,000 projects

14 contracted

$2,500

10.8

$2,000 12

2014+

$1,500

pursuing

$1,000

7.7 $3-$4 billion

8 in additional

$500

projects

$0 6

2003 2005 2007 2009 2011 2013 2015 2017

Transco Gulfstream* Constitution* Capacity*

* Represents Williams’ ownership percentage. The estimated project in-service dates assume timely receipt of all regulatory approvals.

Constitution expected in service late 2015 to 2016.

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Large-Scale, Deepwater Footprint Attracting High-Return Tiebacks

CONTRACTED:

Gulfstar One – Tubular Bells (GS1) – expected online 3Q 2014

Kodiak – tieback to Devils Tower – expected online 3Q 2015

Gunflint – tieback to GS1 expected online 1Q 2016

POTENTIAL:

Appomattox Development (Norphlet Play) – gas gathering, transportation, & processing online early 2019

Taggart – tieback to Devils Tower – online 1Q 2016

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Proposed ACMP/WPZ Merger Would Create Leading Natural Gas MLP

Expected > Expected 2015 distribution increase of at least 25%1 above Access Midstream Partners’ current

Benefits guidance of $2.791 per unit up more than 40%1 vs. current 2014 guidance

> Expected 2016 distributions of at least 20%1 above Access Midstream Partners’ current 2016

distribution guidance

Financial > Best-in-class distribution growth rate of 10-12% through 2017 with strong distribution coverage ratio

estimated to be approximately 1.2x in 2015 and at or above 1.1x through 2017

> Expected 2015 adjusted EBITDA of approximately $5 billion

> Expected strong BBB investment-grade levels

Expected > Creates one of the largest MLPs with leading positions across the three key components of the

Benefits midstream sector:

– Natural Gas Pipelines: Transco, Northwest and Gulfstream represent the nation’s premier interstate pipeline system

– Natural Gas Gathering and Processing: Large-scale positions in growing natural gas supply areas in major shale

and unconventional producing areas

Commercial – NGL and Petrochemical Services: Unique downstream presence on Gulf Coast and in western Canada provides

differentiated long-term growth

and > Combines the stability of Access Midstream Partners’ current contract portfolio with Williams

Operational Partners’ enhanced long-term growth opportunities and development expertise

> Opportunity to further enhance and streamline operations, business-development, commercial and

support capabilities

> Aligns WPZ and ACMP unitholders

> Expected to increase efficiency in capital allocation to growth opportunities

1Assumes merger is consummated in 2014. Cash distributions subject to board approval.

Cash distribution coverage ratio and adjusted EBITDA are non-GAAP measures. Reconciliations to the most relevant measures included in GAAP are provided in this presentation.

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Significant Valuation Re-rating Opportunity

Still Lies Ahead

2014-2016

DISTRIBUTION CAGR

Current

Yield

10%

Median large-cap, diversified coverage ratio is 1.1x

Merged MLP expected to be at or above 1.1x through 2017

KMP WPZ

ETP

EEP

OKS

PAA ACMP2

SEP

4% EPD

Implied re-rating to 2.8%

Pro Forma ACMP / WPZ

0% 5% 10% 15%

Source: Company filings and FactSet as of 8/8/2014

Notes: 1. Based on Wall Street research consensus as of 8/8/2014; 2. ACMP is not included in the regression line; 3. Peer group includes large cap diversified midstream MLPs

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Expect >$25 Billion in WPZ Committed Plus Potential WMB projects

expected to be

Capital Projects 2014-19; Additional $4 Billion dropped down to

WPZ in late 2014

of 2014-16 Growth Capex at ACMP to early 2015

TARGET IN-SERVICE DATES FOR VISIBLE GROWTH PROJECTS

2014 2015 2016 2017 2017+

> Geismar > Constitution > Gunflint > Atlantic Sunrise > Northeast G&P

Expansion Pipeline1 > Northeast G&P > Dalton Lateral > Sabal Trail ownership option

> Gulfstar One > Leidy SE > Parachute > Hillabee > Transco – numerous other

> Keathley > Virginia Plant Expansion Phase 1 expansions

Canyon Southside > Northeast G&P > Gulfstar FPS and pipelines –

Connector > Kodiak U.S., PEMEX

> NE: Frac II > Gulf Trace

> Northeast G&P > Gulf of Mexico – other

> Garden State

> NE: Oak Grove oil-driven services

> Mobile Bay (new)

TXP I South III > Pacific Connector & other

> NE: ethane line NWP projects

> CNRL Offgas

& de-ethanizer Processing > Canadian PDH 1&2 (WMB)

> NE: Other (WMB/WPZ) > Syncrude Offgas Processing

facilities > Gulf Coast(WMB)

> Rockaway Petchem > Geismar 2 (WMB)

Lateral Services (WMB)

In progress

Plus $4 billion2 ACMP Growth Capex Potential/under negotiation

1. Constitution Pipeline expected in-service date range is late 2015 to 2016.

2. ACMP growth capex range is $3.675 billion to $4.075 billion.

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Williams Well Positioned to Participate in Once-in-a-generation Industry Supercycle

WMB now one of the largest publicly traded GP holding companies with control of both WPZ and ACMP

Right long-term strategy at the right time

Ideally positioned assets, sustainable competitive positions

Market dynamics shifting to tailwinds

Hard-wired focus on safe, reliable operations and project execution

Nearly $30 billion of potential growth – disciplined capital allocation

Strong leadership in place to capture the value opportunity

All the Right Ingredients to

Deliver Sustained Value Growth

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Non-GAAP Disclaimer

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Non-GAAP Disclaimer

This presentation includes combined adjusted EBITDA for Williams Partners and Access Midstream Partners for 2015 and cash distribution coverage ratio, which are non-GAAP financial measures as defined under the rules of the SEC.

For Williams Partners L.P. we define adjusted EBITDA as net income (loss) attributable to partnership before income tax expense, net interest expense, depreciation and amortization expense, equity earnings from investments and allowance for equity funds used during construction, adjusted for equity investments cash distributions to partnership and certain other items management believes affect the comparability of operating results.

Access Midstream Partners defines adjusted EBITDA as net income (loss) before income tax expense, interest expense, depreciation and amortization expense and certain other items management believes affect the comparability of operating results.

For Williams Partners L.P. we also calculate the ratio of distributable cash flow to the total cash distributed (cash distribution coverage ratio). This measure reflects the amount of distributable cash flow relative to our cash distribution. We define distributable cash flow as net income plus depreciation and amortization and cash distributions from our equity investments less our earnings from our equity investments, income attributable to noncontrolling interests and maintenance capital expenditures. We also adjust for payments and/or reimbursements under omnibus agreements with Williams and certain other items.

This presentation is accompanied by a reconciliation of adjusted EBITDA to its nearest GAAP financial measure. Management uses this financial measure because it is an accepted financial indicator used by investors to compare company performance. In addition, management believes that this measure provides investors an enhanced perspective of the operating performance of the partnership’s assets and the cash that the business is generating. Adjusted EBITDA is not intended to represent cash flows for the period, nor is it presented as an alternative to net income or cash flow from operations. It should not be considered in isolation or as substitutes for a measure of performance prepared in accordance with United States generally accepted accounting principles

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Net Income After Tax Reconciliation to 2015 Adjusted EBITDA

Williams Access

Partners Midstream Combined*

Low High Low High Low High

Net income after tax attributable to partnership $1,755 $2,105 $ 470 $ 645

Net interest expense 645 665 225 175

Income tax expense 45 55 5 5

Equity earnings from investments(310)(340) —

Equity investments cash distributions to partnership 360 400 —

Depreciation & amortization (DD&A) 1,010 1,060 550 525

Equity allowance for funds used during construction(90)(100) —

Adjusted EBITDA attributable to partnership $3,415 $3,845 $ 1,250 $1,350 $4,665 $ 5,195

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