The USGS released a new assessment of oil and gas potential that includes the extreme NW corner of Arizona, in the Sevier thrust belt. The USGS estimates mean reserves of 301 million bbls of oil (MMBO) and 100 billion cubic feet (BCFG) of natural gas but since the area is predominantly in Utah, we can't tell how much may lie in Arizona.
Last year, my colleagues in the oil business in Utah told me a leasing play was underway in northern Arizona, following the thrust belt discovery by Wolverine Exploration in central Utah. It seems clear this is the target they are after.
The USGS estimates range from 33 MMBO and 10 BCFG (at a 95% confidence level) to 809 MMBO and 279 BCFG (at a 5% confidence level) for the Sevier thrust belt. Only a small part of that is likely to occur in Arizona.
The full report is at "Geologic Assessment of Undiscovered Oil and Gas Resources of the Eastern Great Basin Province, Nevada, Utah, Idaho, and Arizona," USGS Digital Data Series, DDS-69-L, Version 1.0, 2007.