The oil and gas industry doesn't like to talk about its environment and safety record beyond bland assertions that safety is a top goal. But drillers cause more than 6,000 spills each year. Until our investigation, no one had put a figure on it. The records are scattered amid databases, websites and even file drawers of state agencies across the country. EnergyWire spent four months assembling the data for the most comprehensive report yet on the spills that flow from the nation's oil and gas boom.