with our long-term debt obligations. Market risk associated with our fixed and variable rate long-term debt relates to the potential reduction in fair value and negative impact to future earnings, respectively, from an increase in interest rates. We had $9.6 billion of fixed-rate long-term debt and $8.5 billion of variable-rate long-term debt at December 31, 2009. At December 31, 2009, an increase of 100 basis points in average annual interest rates would have decreased the estimated fair value of our fixed-rate long-term debt by $297 million and increased interest expense on our variable-rate long-term debt by $82 million.

Foreign Currency Exchange Risk

     Our results of operations may be impacted by foreign exchange rate fluctuations on the U.S. dollar value of foreign currency-denominated operating revenue and expense. Our largest exposures come from the Japanese yen and Canadian dollar. In general, a weakening yen or Canadian dollar relative to the U.S. dollar results in (1) our operating income being unfavorably impacted to the extent net yen or Canadian dollar-denominated revenues exceed expenses and (2) recognition of a non-operating foreign currency gain due to the remeasurement of net yen or Canadian dollar-denominated liabilities. To manage exchange rate risk, we attempt to execute both our international revenue and expense transactions in the same foreign currency to the extent practicable. We believe changes in foreign currency exchange rates are not material to our results of operations.