Murder, smuggling and organized crime.
At least, that's according to an article over at Business Week which talks to several landowners about the unexpected consequences of oil pipelines including the Vickers family, who found a badly decomposing body along a pipeline that crosses their ranch:
The Vickers ranch is crossed by a steel pipe as thick as a man’s calf. It delivers crude oil from a cluster of south Texas oilfields known as the Vicksburg Fault Zone to refineries in the subtropical waterfront city of Corpus Christi. Like thousands of miles of similar pipelines sprawling across the U.S. Southwest, it has been seized upon by traffickers and smugglers as a good way to evade police and the Border Patrol agents who watch the state highways. These corridors are unmonitored because they stretch across thousands of acres of private property, and law enforcement authorities don’t have the resources to patrol them.
Of course this has little to do with what's inside the pipeline (unless we want to get into how the macro-economic issues of climate change and globalization feed political instability and organized crime), and everything to do with the physical nature of such pipelines—namely they are long, often unguarded, they traverse geo-political boundaries, and they are cleared of scrub on all sides to make sure emergency services can get access. In other words, they're basically an alternative transportation system for people who'd rather not be spotted by the authorities.
Still, it's one more reason for landowners to think twice before allowing an oil pipeline in their backyard.