MarkWest is engaged in the gathering, processing, and transportation of natural gas; the transportation, fractionation, storage and marketing of NGLs; and the gathering and transportation of crude oil.

MarkWest Energy Partners, L.P. welcomes inquiries from investors, news media, business associations, and others interested in the operations of the company.

Summary

This Code of Conduct and Ethics (the "Code") sets forth standards of conduct for all representatives of MarkWest Energy Partners, L.P. (the "Partnership") and its subsidiary companies and affiliates, including the directors and officers of the Partnership's general partner, MarkWest Energy GP, L.L.C., and all the employees and agents of MarkWest Hydrocarbon, Inc. who is the Partnership's service provider and who is the employer of all MarkWest employees.

MarkWest's reputation rests on our ability to act with honesty, integrity, and trustworthiness. To that end, we have adopted and communicated our Code of Conduct & Ethics as the cornerstone of our business.

The Code provides information and guidance about our standards of integrity and explains certain legal and ethical responsibilities. It does not address every specific situation or set forth a rule that will answer every question. Rather, it is intended to provide guidance on our responsibilities and assist employees, officers and directors in making the right decision. The Code is part of MarkWest's Employee Handbook.

Each of us is responsible for complying and encouraging others to comply with the Code. Employees are also asked to ensure that any third party retained on behalf of MarkWest is made aware of the existence and importance of the Code. Please read the Code carefully. You will be asked to acknowledge that you have read it and that you agree to abide by its terms.

Table of Contents

Here is what you will find in the Code of Conduct and Ethics.

Introduction

• Overview
• MarkWest Core Principles
• Asking Questions and Voicing Concerns
• Duty to Report a Concern
• Failure to Comply with the Code

Compliance with Laws, Rules and Regulations

• Legal and Regulatory Matters
• Health, Safety and Environmental Protection
• Investments and Insider Trading Compliance
• Political Processes and Government Relations
• Disclosure Policy

Conflicts of Interest

• Gifts and Entertainment
• Doing Business with MarkWest
• Employment Outside of MarkWest
• Outside Business Activities

Competition and Fair Dealing

Confidentiality

Discrimination and Harassment

• Harassment (Verbal or Physical)
• Sexual Harassment
• Discrimination/Harassment Complaint Procedure

Protection and Proper Use of Company Assets

• Systems Communications
• Maintain Complete and Accurate Accounting Records
• Record Retention
• Comply with Corporate Policies

Your Ultimate Duty to MarkWest

Special Notice for Senior Financial Officers

Administration

• Board of Directors
• Officers and Managers