Cosmo Oil Co., Japan's fourth-biggest refiner, said Wednesday it halted shipments of kerosene from its Yokkaichi refinery in Mie Prefecture after some fuel in a storage tank was found to be contaminated.

Cosmo Oil on Tuesday discovered that kerosene stored in a tank at the 175,000-barrel-a-day refinery had been accidentally mixed with residue, Tatsuya Yano, spokesman for the Tokyo-based refinery, said by telephone Wednesday. The company will resume shipments Friday after cleaning the tank, he said.

Demand for kerosene, a primary heating fuel in Japan, typically declines during summer, spanning late June until early September. The interruption in shipments won't have an impact on Japanese supplies, said oil analyst Ken Hasegawa.