The upper Miocene Potter sandstone reservoir of the Santa Margarita member of the Monterey Formation was deposited in deep water as a coalesced turbidite fan along the west flank of the present day San Joaquin Valley. Contributing over 35 percent of the cumulative production of the giant Midway-Sunset Field, this reservoir is currently producing more than one half of the field’s daily production of 162,000 barrels of oil per day (BOPD). Thermally enhanced oil recovery (TEOR) techniques are routinely used to produce the heavy, viscous oil in these steeply dipping sand packages where gravity drainage is a key factor. Producing since 1910, the field development practices have progressed from conventional primary to cyclic steam to steamflooding and includes some active fire floods. The dynamic continually changing reservoir conditions, due to these recovery processes, add complexity to formation evaluations. With the advent of horizontal drilling this reservoir has been and continues to be one of the most significant at Midway-Sunset Field