The oil companies DONT buy the land they lease it and share the revenue from the oil and/or gas production. First they pay a bonus for signing the lease. This can be a large amount of money depending on the probability of sucess and with fracking this is high. Usually there are a number of companies and individuals competing for these leases and the bidding is active. You are also entitled under the leases to surface damage payments which can be large if you are close to the well site. I read about a man in Texas who had to leave his double wide in the desert when he leased to the oil company. This was sad except for the $500,000 in bonus and damage money he received for signing and the thousands of dollars in monthly royalties he will get.