43 CFR §3206.15

Where the United States owns only a fractional interest in the geothermal resources of the lands in a lease, BLM will only charge you with the part owned by the United States as acreage holdings. For example, if you own 100 percent of record title in a 100 acre lease, and the United States owns 50 percent of the mineral estate, you are charged with 50 acres.