I bought a property that turned out to have a leaking oil tank. It had been leaking for the last 10-15 years. I've owned the property for 1 year, previous owner since 1964 (or so). I have had the contaminated dirt remediated and have a whopping bill. Is the previous owner liable for part or all of the clean up costs? If he is unwilling to pay, can I sue or put a lien on his current property?

Well, working backwards on your question... I highly doubt you'd be able to put a lien on his current property.

As far as your current situation... how did you discover the problem? I assume you got some sort of property disclosure when you purchased the property? Typically in these situations that disclosure is a key element of the case. If the previous owner had NO KNOWLEDGE of the problem, then it would be a roll of the dice to sue him. If you have reason to believe that he knew about it and didn't disclose it, then your case just got a lot stronger. You need proof, though.