Cabot Corp. v. Brown
In Cabot Corp. v. Brown, 754 S.W.2d 104 (Tex. 1987), the Court stated that "under a gas royalty clause providing for royalties based on market value, the lessee has an obligation to obtain the best current price reasonably available." Id. at 106.
But Cabot was decided on the basis of division orders, not whether the implied covenant required the lessee to pay royalty based on the best available price; thus the language in question was not necessary to the decision.
Moreover, as support for the quoted statement, the Court cited a treatise that actually states that a market-value royalty is based on "the best current market price reasonably available." Richard W. Hemingway, Law of Oil and Gas 8.9(C) at 443 (2d ed. 1983)