Thanks for the shout-out, Martha!
(disclaimer: Hi, appraiser/engineer here, but I’m not a tax expert, and please consult your CPA for any tax-specific advice)
Unfortunately, @TennisDaze is right on the money (as per usual :)). Retrospective appraisals establish a higher cost basis than the default “$0” many people start with when they inherit minerals, however you have to establish a market value as of that date. You can’t let the present-day value influence the historical value. It needs to be a conclusion you could have reached as of that historical date, had someone done the proper title research, reservoir analysis, and economic study at the time.
Head’s up for anyone else reading this, there’s incorrect information about how to establish a higher cost basis floating around the internet (shocker, I know). Please be wary of anyone who is interested in selling your minerals and who tells you creative ways to increase your cost basis. They’re just trying to help close a deal. For example, taking today’s sales value and then back-calculating the value on the date you inherited based on inflation, commodity prices, or any other similar benchmark is not an established method for oil and gas historical property values. A good rule of thumb is: was there ANYONE who was remotely interested in paying that price back then? You’re only allowed to step up your cost basis to the market value at the time of inheritance, and oil and gas trapped in the ground is not the same thing as a bar of gold sitting in a dusty closet.
Another rule of thumb I usually use is 2010(-ish) is typically the earliest inheritance date I find it worth the time and effort to do a technical analysis to calculate the remaining reserves value at the time of inheritance. Most assets inherited before then would only have value tied to producing wells, and TennisDaze is also correct that establishing the value as of the date of inheritance is just the first step of saving money on capital gains tax. You also have to account for any depletion you’ve already claimed. To put it simply, if it was worth $100,000 in 1980, you claimed $100,000 of depletion of value over the years, then today’s value SHOULD be $0. Any additional dollar you sell it for today would be considered a capital gain beyond what it was worth when you inherited it.
Why 2010? Because 10-15 years of production tends to deplete most of the value for many assets. Also, this is roughly when the shale boom started, and most people looking to save money on capital gains tax are selling assets in a shale play. Which likely means these same assets were worth next to nothing before the shale boom made the acreage valuable. Yes, the oil was technically there before the shale boom, but it wasn’t something the industry knew how to recover and still make money, so it didn’t have value yet. The secret sauce to crack that code wasn’t figured out yet.
I know that was more than you asked, but we get this question a lot and I wanted to answer for others also.