MarkWest Energy Partners, LP (MWE)

Interest Rate Risk

We are exposed to changes in variable interest rates payable on $85.5 million of borrowings under our credit facility as of September 30, 2005, primarily as a result of our floating interest rates under this facility.  For the nine months ended September 30, 2005, the weighted average interest rate on the credit facility was 6.14%.  The carrying value of the credit facility approximates fair value since the facility bears interest at current market.  As of September 30, 2005 floating rate debt represented 28% of our total outstanding debt.  We may make use of interest rate swap agreements in the future, to adjust the ratio of fixed and floating rates in the debt portfolio.  We also have fixed rate debt of $225.0 million on our senior notes.  The fair value of the senior notes was approximately $222.8 million at September 30, 2005 based on quoted market prices.

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Interest Rate Risk

We are exposed to changes in variable interest rates payable on $65.0 million of borrowings under our credit facility as of June 30, 2005, primarily as a result of our floating interest rates under this facility.  For the six months ended June 30, 2005, the weighted average interest rate on the credit facility was 5.8%.  Borrowings under the credit facility are due in November, 2006.  The carrying value of the credit facility approximates fair value since the facility bears interest at current market.  As of June 30, 2005 floating rate debt represented 22% of our total outstanding debt.  We may make use of interest rate swap agreements in the future, to adjust the ratio of fixed and floating rates in the debt portfolio.  We also have fixed rate debt of $225.0 million on our senior notes.  The fair value of the senior notes was approximately $223.9 million at June 30, 2005 based on quoted market prices.

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Interest Rate Risk

We are exposed to changes in variable interest rates payable on $40.0 million of borrowings under our credit facility as of March 31, 2005, primarily as a result of our floating interest rates under this facility.  As of March 31, 2005 floating rate debt represented 15% of our total outstanding debt.  We may make use of interest rate swap agreements in the future, to adjust the ratio of fixed and floating rates in the debt portfolio.

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