Oil and gas leases that cover larger tracts — say 300 acres or more — should contain a retained acreage clause.
A retained acreage clause has two parts: defining how much acreage will be kept under lease by a well and requiring the lessee to designate that acreage; and defining when the retained acreage must be designated and lands outside the retained acreage tracts released. The idea is to allow the operator to retain the acreage, and only the acreage, being drained by each well.
The amount of acreage (and depths) retained by a well may depend on whether the well is vertical or horizontal; whether the well is classified as a gas well or an oil well; and the depth of the perforated interval. Before the development of horizontal well technology and the ability to produce from tight unconventional formations, retained acreage clauses generally allowed units for oil wells of 40 acres and units for gas wells of 160 acres. For deeper production, units could be 80 acres for oil and 320 acres or even 640 acres for gas. It was generally assumed that a gas well would drain a larger area in a conventional field than an oil well.


