To provide a system and method for supplying fuel, capable of further effectively providing a fuel consumption improving effect in the case of using mixed fuel containing oxygenated compound fuel as fuel for an internal combustion engine.

This fuel supplying system 10 in which at least a part of a fuel component in mixed fuel 55 with oxygenated compound fuel added to hydrocarbon-based fuel is converted into the other fuel component by using a catalyst and supplied to the internal combustion engine 1, is provided with a catalyst retaining part 77 exposing two or more kinds of catalyst beds 31, 32 to the different temperature conditions, and a catalyst bed selection part 80 which selects among two or more catalyst beds 31, 32 the catalyst beds 31, 32 through which mixed fuel 55 is passed according to the load condition of the internal combustion engine 1, and passes mixed fuel through the selected catalyst bed.

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