Abstract: An aqueous organic sulfonate surfactant system containing an alkylpolyalkoxyphenylethersulfonate cosurfactant has a salt tolerance comparable to one containing NEODOL.RTM. 25-3S and has greater heat stability.

Abstract: Oil is displaced within a subterranean reservoir by injecting a combination of substantially liquefied CO.sub.2, brine and surfactant material into the reservoir, with the surfactant material being a polyalkoxy aliphatic sulfonate surfactant material which has specified dispersing and partitioning properties in contact with the brine and the fluids in the reservoir at the reservoir temperature and a pressure sufficient to substantially liquefy the CO.sub.2 within the reservoir.

Abstract: A process of recovering oil from a subterranean reservoir in which the oil is acidic but forms monovalent cation soaps of only relatively low interfacial activity when reacted with aqueous alkaline solutions, comprises displacing the oil toward a production location with a mixture of gas and cosurfactant-containing aqueous alkaline solution.

Abstract: The injectivity of an oil-containing reservoir is increased by injecting successive portions of a solution or slightly turbid dispersion of reservoir-tailored amounts of polyalkoxyalcohol sulfate surfactant and lower alkanol in highly saline aqueous liquid and a reservoir acidizing solution.

Abstract: Portions of a subterranean reservoir are temporarily plugged by injecting an aqueous liquid solution which contains nitrogen gas-generating reactants, a foaming surfactant and a pH controlling system arranged so that the solution remains relatively unreactive within the well but forms a relatively immobile foam within the pores or other openings within the reservoir formation.

Abstract: In an oil reservoir in which the water contains more than about 9% dissolved salt, oil is produced by injecting an oil-displacing dispersion of at least one surface active alkylaryloxy polyethoxyethane sulfonate in the reservoir water or an equally saline water followed by a mobility controlling dispersion of noncondensible gas in an equally saline water.

Abstract: A process for recovering oil by successively injecting at least a chemical slug containing an active aqueous surfactant system or thickened aqueous liquid and an aqueous drive liquid into a reservoir having a significant amount of ion exchange capacity, is improved. The ionic composition of each injected fluid is arranged to provide a ratio, between the concentration of its effectively predominate monovalent cation and the square root of the concentration of its effectively predominate divalent cation, which ratio at least substantially equals such a ratio within the aqueous fluid immediately ahead of the injected fluid.