The Fillmore field is a relatively minor Ventura basin oil field located west of and adjacent to the city of Fillmore. It is one of several recent discoveries in the Santa Clara Valley area between the Oak Ridge fault on the south and the San Cayetano fault on the north.

The Fillmore field is an excellent example of multiple-zone primary stratigraphic trap accumulation, independent of local structural closure. Two middle Pico (Pliocene) sand zones have produced to date. Closure in both zones is effected by rather abrupt updip pinch-out on a low southeastward-dipping homocline.

The Spalding pool was discovered by Standard Oil Company in April, 1954, and development of the field has been continuous and orderly since then. The Perkins pool, slightly shallower but more limited in areal extent, was discovered by Humble Oil and Refining Company in January, 1957. Both zones have short oil columns, small free gas caps, level water tables, and relatively narrow productive areas elongate essentially parallel with the regional northeasterly strike.

At present the field is 3 miles long and has maximum width of 3,200 feet, with a proved productive area of approximately 800 acres. Average well depth is a little more than 14,000 feet, and gravity of the oil is 27°-35° API. Cumulative production to August 1, 1957, was 2,387,000 barrels, and average production as of that date was 7,984 B/D from 22 wells.

The productive limits of the two known pools have been fairly well established except at the east end of the field, where development is continuing at present. Future expansion of the field depends on its easterly extent and possible discovery of additional Pliocene sand pinch-out traps.

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