Mount Poso lies in the Sierra Nevada foothills of Kern County, directly north of the Kern River field, running about nine miles long and four to five miles across. Discovered in 1926, it was a modest producer for four decades before Shell Oil acquired it in the 1960s and applied steam flooding at scale, taking output from around 1,560 barrels a day in 1969 to roughly 25,000 by the 1980s. Cumulative production has been reported close to 300 million barrels, making Mount Poso one of California’s notable heavy-oil successes.
The field was discovered in 1926, in the middle of the decade that also opened Round Mountain and Poso Creek along the same foothill belt. Its oil is heavy — 13 to 16 degrees API with roughly 0.65 percent sulfur — and its reservoirs are shallow, with the deepest well in the field reaching only about 3,759 feet. Under primary production those characteristics meant low rates and quick disappointment, and Mount Poso spent its first forty years as an unremarkable Kern County producer.
Shell Oil bought into the field in the 1960s specifically to apply thermal recovery, and the results were dramatic. Daily production rose from about 1,560 barrels in 1969 to roughly 25,000 barrels by the 1980s, and annual output peaked in 1981 at over nine million barrels, which made Mount Poso the eighth most productive field in California that year. Few fields illustrate as cleanly what steam does to a shallow heavy-oil reservoir, or how completely it can rewrite a royalty owner’s expectations.
Shell sold to Nuevo Energy in 1999, and Nuevo later became part of Plains Exploration and Production. Vintage Production, an Occidental Petroleum subsidiary, acquired positions in 2006 and had become the largest operator by 2009. Production had by then fallen back to roughly 554,000 barrels a year from 652 active wells — a long steam-supported tail rather than a collapse. That trajectory of a forty-year primary lull, a thermal boom, and a slow decline is the shape most Mount Poso royalty histories follow.
Mount Poso produces from the Oligocene Vedder Formation and the Miocene Freeman-Jewett section on the eastern margin of the San Joaquin Basin, where sediments thin against the Sierra Nevada. The reservoirs are shallow: the deepest well in the field reached about 3,759 feet, into the Eocene Freeman. Oil is heavy at 13 to 16 degrees API with roughly 0.65 percent sulfur, biodegraded by shallow burial and circulating groundwater. Shallow, thick, laterally continuous sand holding viscous oil is close to ideal geology for steam.
Mount Poso is a steam flood field, and its history is the argument for the technique. Continuous steam injection heats the Vedder sands until 13-gravity crude will flow to closely spaced producers, and the same reservoir that yielded about 1,560 barrels a day under primary production yielded roughly 25,000 under steam. Because steam generation burns natural gas, project economics depend on the oil-to-gas price relationship, and injection is permitted through CalGEM. Royalty volumes rise and fall with the steam program, not with the rock.
A Mount Poso royalty is thermal income: slow-declining, long-lived, and contingent on continued steam injection by whichever successor operator holds your lease. Ownership has passed from Shell to Nuevo to Plains to Vintage and Occidental, so tracing an interest often means working back through several payor names. Valuation should weigh recent lease-level volumes and the operator’s demonstrated commitment to the flood rather than the field’s peak-year statistics. We buy minerals and royalties in Kern County and provide free written offers.
County-level well data, production charts, and selling guides for the counties this field spans:
Production went from roughly 1,560 barrels a day in 1969 to about 25,000 barrels a day by the 1980s after Shell applied steam at scale, with annual output peaking in 1981 at over nine million barrels. Very little of that oil would have been recovered under primary production.
The field has passed from Shell to Nuevo Energy in 1999, then into Plains Exploration and Production, with Vintage Production, an Occidental subsidiary, acquiring positions in 2006 and becoming the largest operator by 2009. Check your division order for the current payor on your leases.
Not necessarily. Steam floods decline gradually and respond to injection schedules, oil price, and natural gas cost. The field still had hundreds of producing wells well after its peak. Lease-level data tells you far more than the trend of a few statements.