About 40 Montana landowners have reported contamination of their property by crude oil spilled from a ruptured Exxon Mobil pipeline into the flood-swollen Yellowstone River over the weekend, the company said on Wednesday. As the scope of property damage came into sharper relief, Montana’s governor accused Exxon of underestimating how much oil spewed into the one of America’s most pristine rivers 150 miles downstream from Yellowstone National Park.