First of all, congrats on taking the time to understand the value of your minerals. You have the power in this situation so definitely shop around. In general, my advice would be to not sell unless you need the money now. Another thing that some people don't realize is that even if you sell you don't have to sell ALL of your mineral rights.
The value associated with your minerals is based upon the likelihood that oil & gas will be found if a well is drilled. Assuming there is enough nearby activity, this can be determined by looking at nearby production (offset wells) to look at trends based on location. From there, multiple wells are reviewed to develop what is called a type curve which represents the rate of production from a future well (in an area with certain characteristics) over time. These "type curves" are used to forecast expected production rates from wells that might be drilled based on current well spacing in the area. Then, the expected cash flows are forecast over time based on when it is expected for these wells to come online, what your net revenue interest is, and what oil and gas prices are expected to do over time. This "discounted cash flow analysis" will yield a number or Net Present Value which represents what your minerals are worth today based on future cash flows that take into account these variables and how much future cash flows are discounted to today's $. As you can imagine, a well that is drilled in a well understood and mature basin is generally a lower risk than a "wildcat" exploration well that is drilled in an emerging play. As such, buyers will generally risk these situations differently and all things considered are likely to pay a bit more for the sure thing vs. an uncertain outcome.
At the end of the day and especially if there is not a lot of activity to perform a credible analysis of potential reserves, then you have to rely on what the market is willing to pay for minerals. If there are a lot of permits to drill exploratory wells in an area, there will be higher demand for minerals (and they will command a higher price).
Since market value varies greatly by location and is also hard to come by, it pays to shop around. If you can afford it, get an appraisal on your property so that you are at least armed with this knowledge. Then, do the research on the activity level in the area through sites like the OCC website (see below for how to do this). You can then be equipped with the requisite knowledge to demand the best price.
In terms of understanding what type of activity is going on nearby, I would recommend doing a search via the legal description of your tract (e.g. section township range) via the Oklahoma Corporation Commission website Oil and Gas division. From there scroll down to Oil and Gas Data Mining. You can choose to view data on a map (GIS Data Mining) or perform a text based search. In either, click on "Switch to Advanced Filter" to search by Section, Township, Range. There you can view production and well documents. The OCC website production data availability can be spotty so if it doesn't show anything you can go to the Oklahoma Tax Commission Website and perform a search by legal description there and if there is production it should be listed.
In addition to shopping it around to different buyers, if your interest is large enough and you are willing to pay a commission to list it and get it in front of as many buyers as possible there are auction websites out there that can do this (for a fee).
These are general tips and every situation is different so check with someone qualified to help with an independent appraisal if you can.
I hope this helps.