Moorings:
Congratulations on receiving good proposals for the land you have. Can we assume that your land while located in a good location is currently idle and is unused?
I would strongly recommend that you do not sell the land, but that you lease it to the oil companies on long term leases. The reasons for this are:
1. The remaining land that they do not buy cannot be used for any other purpose because the soil may be contaminated by oil, petrol, etc.
2. The remaining land will be at a risky location as no one may want to build residential accommodations next to a petrol station due to the risk of fire.
3. New associated businesses will come up next to the petrol station. For example, a restaurant, a mini-supermarket, a car repair shop, etc. These would be constructed on your land and thus you would get new revenue streams from the owners of these businesses.
4. By being the landlord of the petrol station, you are guaranteed income for the long term. If a particular brand sells the petrol station to a competitor, you still continue to receive your rental income (regardless of who the tenant is).
5. Due to the long term nature of the lease, you may use the guaranteed rental income as an income stream for you to get a loan from a bank for you to do something else.
6. The oil company will make alot of investment in the infrastructure of the petrol station: the buildings, the fuel tanks, the licensing, the branding, etc. They would rather comply with your letting demands rather than walk away from their heavy investment. Being the landlord, you will pull the strings of the entire business.
To summarize, in my opinion, you would get more rental income and influence in the long term than you would benefit by selling the land.
BTW If 2 companies have approached you, then others would be interested. If I were you, I'd write a proposal (including pictures) inviting other oil companies to lease the land. I'm sure a few would respond favorably preferring to lease the land rather than buy it.
In answer to your question of what you should look out for, I'd say you should look out for the company that sounds flexible and willing to lease the land rather than outright buy it.
-Fair Car Dealer