Budget airline Norwegian Air Shuttle's fare yield fell in May due to growth in its lower-yielding international traffic, but its total traffic volume rose sharply, the airline said on Tuesday.

Norwegian, a small rival to Scandinavian carrier SAS, estimated its yield -- or average revenue per passenger carried and kilometre flown -- at 0.70 Norwegian kroner (USD$0.109) in May, down from 0.74 in April.

"The yield development is related to changed mixture of international and domestic traffic with an increased portion of international traffic and increased sector length," Norwegian said in a statement. "Yield in the domestic market increased about five percent from April 2005."

Total passenger traffic, also known as revenue passenger kilometres (RPK), rose 73 percent in May year-on-year, Norwegian Air Shuttle said. The rate of growth picked up from April, when RPK rose 54 percent from the same month a year earlier.

Total passengers carried rose 52 percent in May from a year earlier to 309,229.

The airline's cabin factor, a measure of capacity utilization, was 78 percent in May, up from 69 percent in the same month a year earlier.