As a basis for this bold statement, I refer to a fact sheet produced by the US Geological Survey titled "Reserve Growth Effects on Estimates of Oil and Natural Gas Resources." From the report:
"Operators of oil and gas fields in the United States are required to report total annual production and an estimate of proved reserves from each field to the U.S. Department of Energy. These two quantities provide an estimate of the petroleum volume that ultimately will be recovered from a field. Experience shows that over the life of many oil and gas fields, these estimates of ultimate recovery will increase."
As an example, the report describes "reserve growth for the Midway-Sunset oil field in California"...
"By 1968, 56 years after discovery of the Midway-Sunset field, cumulative production
totaled about 1 billion barrels of oil, and proved reserves—the amount of resource
known with a high degree of certainty to be available for future production—stood at about 200 million barrels. Ultimate recovery was estimated then at about 1.2 billion barrels. Just 8 years later, in 1976, cumulative production exceeded this estimate of ultimate recovery, proved reserves stood at 400 million barrels, and ultimate recovery was set at 1.65 billion barrels. Twenty years later in 1996, cumulative production had reached 2.3 billion barrels, proved reserves stood at about 500 million barrels, and ultimate recovery was set at 2.8 billion barrels. Over a period of 28 years, long after the discovery of the field, estimates of ultimate recovery more than doubled, from 1.2 billion barrels to 2.8 billion barrels. While this example describes the reserve growth of a very large and somewhat atypical field, the general phenomenon of reserve growth is common to fields of all sizes and types."
The report concludes by stating that "Recent estimates incorporating reserve growth suggest that the world’s ultimate supply of petroleum might be larger than has been generally appreciated."