It's not a 13% dividend. The last distribution payout was a one-time higher amount due to settling of some accounts by Semgroup. If you are calculating the yield you need to back out the extra one-time amount and you get an 8-9% yield. Not bad, but not 13%.
As of Jan 1, 2011 MVO will be selling it's oil without hedge contract pricing. They'll be getting NYMEX market pricing, less a wellhead discount of $7.25/barrel. To put in perspective, MVO averages $60/barrel for their oil now with hedge contracts in place. Oil priced above this price will generate a larger dividend, how large depends on the price of oil. This is a good time to get in.