As Scott mentioned, it's different in every county -- and every state.  I've done oil/gas in his fair state (I lived in a hotel in Altoona for a year) as well as Michigan, Ohio and West Virginia.  Hillsdale County Michigan -- which I believe is the only county left with its complete tract index still free to the public -- has all its oil/gas info mixed in with everything else.  Same for Lenawee County which prior to about 30 years ago, must be entirely grantee/grantor.   Because every state is different (Michigan has dormancy laws; Pennsylvania doesn't -- that kind of thing), there is really no definitive book out there.  As with abstracting in general, the best way to learn is to be mentored by someone else.    I firmly believe that any good mortgage abstractor can make the switch to oil/gas (and I have, in fact, encouraged at least 2 people that contacted me to give it a try and they have succeeded).  You can learn what you need from the title people already working a project and then the skills you've used for years will get the work done.  Once you have even a toe in the door, you'll be able to find work.  (It's just hard NOT playing beat the clock every day -- sometimes a single search can take months because of the amount of land it covers and you can make yourself nuts thinking you need to be done in a week!)  Somewhere I have a very old general info book.  When I find it, I'll post the name here on Source of Title.