Neb. Rev. Stat. § 72-307: Neb. Rev. Stat. § 72-307

The lessee may have a right to the renewal of the lease upon the same terms as provided in section 72-303 , so long as such minerals or other valuable substances are produced in paying quantities; Provided, such leases shall in no instance contain any provision abridging the rights of future legislatures to make such laws as may in their judgment be necessary to conserve the interests of the state. If the lessee shall have made extensive tests, or a showing satisfactory to the Board of Educational Lands and Funds that he has proceeded in good faith, even though no successful production has resulted, the board may, upon such showing, grant an extension or renewal for further prospecting.