Oh she was kidding plus it was on Fox so it isnt true. There you go Pocket I already said it for you.
Kinda hard to say if she was kidding, being sarcastic, being serious, or threatening to stab the oil companies in the back.
First, some background. The video is from early 2008, back when oil prices were rising sky high. So basically this is old stuff, nothing new.
Second, congress was trying to address high oil prices with the oil companies. Basically oil companies thought demand was through the roof (we later found out that demand was actually falling during this time, not rising), and came to Washington begging for more leases for drilling. Waters wanted a guarantee from oil companies that if they allowed more drilling, then oil companies would lower prices. If they didn't (basically if they broke their promise), then she would be in favor of nationalizing those companies.
Truth be told, it was all for nothing. The oil companies weren't in control of pricing to begin with, so they didn't have the power to promise lower prices if drilling was opened up. Second, what Waters said could be taken as serious, as a threat, or as sarcasm. However, since nothing happened (no nationalization of oil companies occurred here in the U.S. since that video was originally aired), it's all Washington smoke and mirrors anyway. Plus, it didn't seem that democrats or other "liberals" in Washington were very supportive of her statements anyway.
Personally, I'm not losing any sleep over it because it's a dead issue, and been dead for a while now.