This excerpt taken from the CHK 10-Q filed May 11, 2009.
Change in Accounting Principle
On January 1, 2009, we adopted and applied retrospectively FASB Staff Position No. APB 14-1, Accounting for Convertible Debt Instruments That May Be Settled in Cash upon Conversion. As a result, our prior year condensed consolidated financial statements have been retrospectively adjusted. See Note 6 for additional information on the application of this accounting principle.