O-Ring

OA (logging)

OA (well design)

OAP

OBR

Observation Well

OC

OBS

OCS

Octane

OCTG

OD

OD/ID

Off -pattern Well

Offset Well

Offshore Well

Offshore Platform

OFP

OGIP

OGLV

OGP

OHFP

OHGP

Ohm

welcome

Oil Based Mud

Oil Column

Oil Emulsion Mud

Oilfield Services

Oil-In-Place

Oil-in-Water Emulsion

Oil Jar

Oil Pool

Oil Run

Oil Sand

Oil Saturation (reservoir)

Oil Saver

Oil Shale

Oil-Water Contact

Oil Wet Rock

OIM

OIP

OIW

OJ

OJT

Oleofinic Hydrocarbon

Oligocene

On-Pump

On Structure

On-The-Fly (in mixing)

OOC (North Sea)

OOIP

OOS

Oolite

OP (gas lift)

OPEC

Open Flow Potential

Open Hole Completions

Open Hole Gravel Pack

Open Hole Log

Open Hole Packer

Open Hole Perforating

Open Shoe

Opening Ratio

Operating Gas Lift Valve

Operator

OPEX

Ordovician

ORF

Organic Acid

Organic Deposit

Organic Theory

Oriented Perforating

Orifice Meter

Orifice Plate

Orifice (gas lift)

Orogeny

Orphan Wells

OS

OSHA

Osmosis

OTC

Ottawa Sand

Outcrop

Outer Continental Shelf (MMS)

Outgassing

Ovality

Ovality Limit (CT)

Overbalance

Overburden

Overflush

Overlap

Overlift

Overpull

Overriding Royalty Interest (contract)

Overshot

Overthrust

OWC

OWR

Oxidizers

Oxygen Activation Survey