Petrophysics (from the Greek πέτρα, petra, "rock" and φύσις, physis, "nature") is the study of physical and chemical rock properties and their interactions with fluids.

A major application of petrophysics is in studying reservoirs for the hydrocarbon industry. Petrophysicists are employed to help reservoir engineers and geoscientists understand the rock properties of the reservoir, particularly how pores in the subsurface are interconnected, controlling the accumulation and migration of hydrocarbons. Some of the key properties studied in petrophysics are lithology, porosity, water saturation, permeability and density. A key aspect of petrophysics is measuring and evaluating these rock properties by acquiring well log measurements - in which a string of measurement tools are inserted in the borehole, core measurements - in which rock samples are retrieved from subsurface, and, less frequently, seismic measurements. These studies are then combined with geological and geophysical studies and reservoir engineering to give a complete picture of the reservoir.

Gary John Fox (born December 23, 1943 in Picton, Ontario) is a former politician in Ontario, Canada. He was a Progressive Conservative member of the Legislative Assembly of Ontario from 1995 to 1999.

Fox was educated at the University of Guelph, and graduated from their Advanced Agriculture Leadership Program. He worked as a farmer after graduation, and became a senior partner in Fox Farms of Bloomfield, Ontario. He also served as a councillor on the Sophiasburgh township council and the Prince Edward County Regional Council, and was a reeve of Sophiasburgh.

He was elected to the Ontario legislature in the 1995 provincial election, defeating Liberal Robert Gentile by over 6,000 votes in the riding of Prince Edward—Lennox-South Hastings. (Incumbent New Democrat Paul Johnson was third.) He served as a backbench supporter of Mike Harris's government for the next four years, and was chair of the PC Rural Caucus Advisory Committee. Fox was regarded as one of the most socially conservative members of the PC caucus.