I got this information from another website, I hope it clears up some questions. IT WAS POSTED BY A CERTIFIED PROFESSIONAL LANDMAN.
In Louisiana mineral law, oil and gas is considered a fugacious mineral. Fancy word meaning migratory. Oil and gas migrates through the rock formations to the wellbore and comes to the surface. Oil and gas in the ground are not owned until captured. Which means a well needs to be drilled to capture it into a tank or a pipeline. Its only value in the ground is what someone is willing pay for it... and that it's even there in commercial quantities is not determinable until it's drilled. It's not captured until drilled and there is much risk involved to capture it and even more risk to keep it coming.

It's not like real estate, which can boast the legal term lesion for rescision beyond moiety. That means something like "cancelling a contract due to being paid less than half the current market value." Because market value can be determined in real estate. It's stated in each contract. Thus, an appraiser can give you market value for land. (Which is highly variable if mineral rights are involved along with the land.)

For oil and gas, nope. The value is whatever someone will pay you. Which is highly speculative and open to much interpretation. Also, it largely cannot even be determined. (Back to the principle of capture.) Value is simply a buyer's willingness to pay x-amount.