This excerpt taken from the CHK 8-K filed Nov 1, 2005.
Foreign Currency Exchange Rates
The conversion of the functional currency of Columbia Natural Resources Canada, Ltd. (a Canadian company) in Canadian dollars to the reporting currency of U.S. dollars is based upon the exchange rates in effect at the reporting date while the statements of operations are translated at average rates. The exchange rates in effect at December 31, 2004 and 2003, were $1.20 and $1.29 Canadian dollars to the U.S. dollar, respectively. Exchange gains and losses are included in accumulated other comprehensive income (loss).