You should read this forum for what mineral rights are bringing. Offers you might have received in the mail could be half of what you can get.
If you post the location of your mineral rights there are a lot of knowledgeable people that are familiar with the market.
I would talk to an attorney that handles leasing in Kingfisher. He should know what leases were going for in 2011 and be able to advise you on what you can get. I used Ralph Harrison in Kingfisher.