YOKOHAMA, Japan: Embarrassed Japanese government officials conceded today that they had drastically over-estimated the oil spilled in Tokyo Bay by a factor of 10. Instead of the 100,000 barrel-leak they reported Wednesday when the 147,012-ton tanker ran aground, they now believe only 9,800 barrels poured into the harbor. The 100,000 barrel estimate would have made the accident the worst oil spill in Japan's history. Prime Minister Ryutaro Hashimoto said today most of the oil which spilled from the third of the ship's tanks "seems to have flowed into the second empty tank and miraculously didn't leak outside.'' Still, the slick poses a threat to marine life in the area. By early Thursday it covered an area of the bay about 9.4 miles by 11 miles and was moving westward, rather than north toward Tokyo. TIME's Satsuki Oba reports the news caused residents of the city to breathe an enormous sigh of relief. But not everyone was bursting with joy. Early this morning, a severed ox head was found on the front steps of the house where the tanker company president lives.