A burner includes separate fuel and oxidant conduits. The fuel conduit has inlet, transitional, and outlet sections, and the oxidant conduit has inlet and outlet sections. The cross sectional flow area of the fuel transitional section varies from an initial cross sectional flow area at the fuel intake to a different cross sectional flow area at the fuel outtake, and the cross sectional flow area of the fuel outlet section is substantially uniform. At least some of the oxidant inlet section is spaced around substantially all of at least a portion of at least one of the fuel inlet, transitional, and outlet sections. The cross sectional flow area of the oxidant outlet section is less than or equal to the cross sectional flow area of the oxidant inlet section and is substantially uniform, and at least some of it is spaced around substantially all of at least a portion of the fuel outlet section.