Landowners generally only have rights to the surface of the land. In most cases, this means that even if minerals, oil or gas is under your land, you might not have the right to extract or access those resources even if you do own the land. This could have serious implications if you are planning on selling those resources or selling the rights to those resources. Perform a mineral rights check before negotiating those resources to an interested party.
Check the title to your land. The first place to check and see whether you have the mineral rights to your land is to look at your property title. Some property titles will explicitly say you own the mineral rights. Others will explicitly say you do not own the rights. If you get a definitive answer here, than you search is finished. If your title is silent as to your rights, continue.
Find the original owner of the land and check his deed. If your deed is silent as to your mineral rights, you will probably have to find the original deed and check that deed's information. To do this, visit your county clerk's office where the land records are stored. Inform them that you wish to trace your title back to the original owner. The county clerk will then assist you through the search. Once the original deed is located, check that deed for information regarding mineral rights similar to what you looked at in Step 1.
Hire a landman or a mineral rights attorney. If you cannot locate the rights on your own using the above steps, an expert might be needed. Landmen and mineral rights attorneys specialize in determining the rights of landowners' with respect to the minerals on their land. The price range varies according to jurisdiction but you can probably expect to pay anywhere between a couple hundred dollars to over a thousand.