gas prices typically rise. Natural gas is used by half of U.S. households for heating and to generate 26 percent of the country's electricity. Natural-gas prices rose during an unusually cold November, but December warmed, and temperatures for the rest of the winter are expected to be near normal, which could keep prices low through the spring, analysts expect. On Tuesday, natural-gas futures rose slightly to $3.15 per 1,000 cubic feet (28.3 cubic meters), down from almost $4.50 in late November.