I've been updating my file on oil and gas companies, their reserves and their market cap and enterprise values (EV). (The file includes 65 companies.) While the range of EV to proven reserves is large globally, the range for large companies in the Permian basin is much smaller. Mergers and acquisitions are probably the most telling examples. In M&As the buyers and sellers are both knowledgable. In all M&A cases the purchasing companies are basically just buying reserves, preferably close to their existing infrastructure. In several cases they said as much. For example, Vicki Hollub said that about OXY's purchase of Crown Rock at $22/barrel of oil equivalent (boe) of proven reserves.

finance.yahoo.com - Crownrock acquisition perfect fit growth

This buying of reserves goes for Occidental's purchase of Anadarko, and now of Crown Rock, Exxon's purchase of Pioneer Natural Resources and Chevron's purchase of Hess.

Of the companies we have been discussing, XOM, CVX and OXY, Occidental is currently the cheapest on an EV/proven reserves basis at #20/boe of proven reserves. The most expensive is ExxonMobil at $28/boe. The most expensive acquisition on that basis was Occidental's purchase of Anadarko at $38/boe of proven reserves.