North Dakota has the most reported oil spills of any state. Oklahoma ranks number two, but that may be a gross understatement. State Impact Oklahoma says spill reporting requirements vary from state to state. The Oklahoma mandate is ten gallons or more, Texas is five, and in North Dakota, it's one gallon or more.
Another oil issue is pipelines. State Impact Texas has a three part series looking at the the application of eminent domain. Does a landowner have the right to say no to pipelines?