Oil Initially In Place - OIIP

The amount of crude first estimated to be in a reservoir. Oil initially in place differs from oil reserves, as OIIP refers to the total amount of oil that is potentially in a reservoir and not the amount of oil that can be recovered. Calculating OIIP requires engineers to determine how porous the rock surrounding the oil is, how high water saturation might be and the net rock volume of the reservoir.

Determining oil initially in place is one of the major components undertaken by analysts determining the economics of oil field development. Oil operations do not typically recover the entire amount of oil that a reservoir may have available, meaning that not all fields will be economical unless oil prices warrant the effort.