A friend just brought a lease over to review. I don't know if it is normal, but in legalese language, it says...paraphrasing "If these mineral rights being leased are to be sold, the company has the right to first refusal to purchase the minerals by matching the offer". Also says something to the effect that the offer must be from a qualified company and the offer certified, bla, bla, bla.
Just thought it was unusual to be in a lease, but maybe not. It was in the first part of the lease that everyone says is the "standard" looking lease. In my research I found the below information and link.

Here is an interesting read for understanding the "basics" of leasing.

This article is intended to provide practical advice for landowners in negotiating
oil and gas leases of their mineral interests. It is not a comprehensive list of all possible
issues that may arise in negotiating leases, nor is it a survey of the law concerning
interpretation or enforcement of leases. Landowners are encouraged, where possible,
to consult with attorneys familiar with oil and gas law. The summary below will be
helpful to landowners in discussing with their legal counsel the issues important to them
in negotiating leases of their land. CONTINUED IN LINK BELOW.
http://gdhm.com/images/pdf/jbm-ogleasechecklist.pdf