Carter County, OK Lease in Sec 26, Township 5S, Range 3W

I posted this over in the Carter County, OK group but thought I would put it over here as well in case anyone else can provide some help as well:

Hi, our family received an offer for Lease in Sec 26, Township 5S, Range 3W and I was hoping someone could help me with how I can determine what the going rate for amount per acre is in this area.

Also, does anyone know if there is some drilling activity occurring in this area?

I understand from the landman that this is a "top lease" and I am not familiar with what that means so any help defining that for me would be so appreciated.

Lastly, there is an Exhibit "A" attached to the lease that I don't really understand. In the second paragraph it reads: "In the event this lease is extended by commercial production beyond its primary term, then on such date this lease shall terminate as to all rights one hundred feet and more below the stratigraphic equivalent of the base of the deepest penetrated formation in the well or wells located on the leased premises, or land unitized therewith. If Lessee is in the process of drilling or completing a well at the end of the primary term of this lease, this clause shall become effective upon conclusion of such operations." This doesn't seem like a good thing to sign as it seems we would be giving up a lot but I am not sure.

Thanks for any help you can provide.....