It looks like the old style language where the usual royalty was 1/8 and thus half of the usual mineral interest in oil would give the owner of that portion a 1/16 interest in the sale of the oil. Most old leases had language stating that the owner was to be paid 1/8 of the proceeds of the oil and either a flat rate, such as $300 / year per gas well, or 1/8 of the proceeds of the sale of the gas. If I had to guess, I would say the wording you quoted is for a conveyance of a half interest in the oil and gas. HOWEVER, I am not a lawyer and am curious if someone has better information that that.
IS this the language in a lease or mineral deed . The difference would greatly change the meaning.. First if it is a lease you must go back and find the mineral deed. Then find out if the minerals were pooled with another property. A mineral deed usually talks about acres of mineral and does not split oil or gas. So my guess you have a lease that was pooled at one time with another property find the mineral deed. If none find out if the minerals were sold off or split in a estate or did you buy the land fee simple. What you indicate by stating the royalty is usually found only in a lease. If the lease is no longer in effect then the mineral title is the determining factor.. I am not a lawyer and just a producer so no legal advise is tendered or implied.
The original question says it was a deed. I have seen a few deeds with similar language, and have wondered what the interpretation of this type of language is. It could vary by state. What I have seen is West Virginia. There was a lot of selling off of half of the oil interest in the 1890s, from what I saw. But sometimes there was no mention of the gas. Since the standard for leasing was that the mineral owner received 1/8 of the sale of the oil, and then either a flat rate annual amount for the gas or a 1/8 of the gas, when selling half of the oil interest, there was the idea of selling the equivalent of the 1/2 of the 1/8 royalty on oil. Technically there is a difference in selling a royalty amount and selling the mineral interest. I hope someone with more knowledge than I can add something here.
If that's a West Virginia document you can make an argument that it's a reservation of 1/2 of all the mineral rights. If it's not, I can't help you because I'm only licensed in West Virginia. Even if it is a West Virginia document, you might have some trouble convincing a judge that that's what it means. The best way to determine what that reservation means is to take a look at the other documents that the parties to that document signed later on that piece of property. If they signed leases or deeds or wills or anything like that they may have used a different phrase to describe what they were transferring, and that would be an indication of what the intent of those parties was when they signed the document. I hope that makes sense......it's a bit of a mess here in WV.