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OCTANE NUMBER - expression of the anti-knock properties of a gasoline, relative to that of a standard reference fuel. There are two distinct types of octane number measured in the laboratory: Research Octane Number (RON) and Motor Octane Number (MON), determined in accordance with ASTM D 2699 and D 2700 respectively. Both the RON and MON tests are conducted in the same laboratory engine, but RON is determined under less severe conditions, and is therefore numerically greater than MON for the same fuel. The average of the two numbers - (RON + MON)/2 - is commonly used as the indicator of a gasoline’s road anti-knock performance. The gasoline being tested is run in a special single-cylinder engine, whose compression ratio can be varied (the higher the compression ratio, the higher the octane requirement). The knock intensity of the test fuel, as measured by a knockmeter, is compared with the knock intensities of blends of isooctane (assigned a knock rating of 100) and heptane (with a knock rating of zero), measured under the same conditions as the test fuel. The percentage, by volume, of the isooctane in the blend that matches the characteristics of the fuel test is designated as the octane number of the fuel. For example, if the matching blend contained 90% isooctane, the octane number of the test fuel would be 90. In addition to the laboratory tests for RON and MON, there is a third method, Road Octane Number, which is conducted in a specially equipped test car by individuals trained to hear trace levels of engine knock.

OCTANE REQUIREMENT INCREASE (ORI) - the tendency of gasoline engines to require higher octane fuels as combustion chamber deposits accumulate.

OILINESS AGENT - polar compound used to increase the lubricity of a lubricating oil and aid in preventing wear and scoring under conditions of boundary lubrication.

OIL MIST LUBRICATION - type of centralized lubrication that employs compressed air to transform liquid oil into a mist that is then distributed at low pressure to multiple points of application. The oil mist is formed in a “generator”, where compressed air is passed across an orifice, creating pressure reduction that causes oil to be drawn from a reservoir into the airstream. The resulting mist (composed of fine droplets on the average of 1.5 microns) is distributed through feed lines to various application points. Here, it is reclassified, or condensed, to a liquid, spray, or coarser mist by specialized fittings, depending on the lubrication requirements. Oils for use in a mist lubrication system are formulated with carefully selected base stocks and additives for maximum delivery of oil to the lubrication points and minimal coalescence of oil in the feed lines.

OLEFIN - any of a series of unsaturated, relatively unstable hydrocarbons characterized by the presence of a double bond between two carbon atoms in its structure, which is chemically active and provides a focal point for the addition of other reactive elements, such as oxygen. Due to their ease of oxidation, olefins are undesirable in petroleum solvents and lube oils. Examples of olefins are: ethylene and propylene. See hydrocarbon, unsaturated hydrocarbon.

OPEC (ORGANIZATION OF PETROLEUM EXPORTING COUNTRIES) - group of oil-producing nations founded in 1960 to advance member interests in dealings with industrialized oil-consuming nations. The 13 OPEC members are: Algeria, Ecuador, Gabon, Indonesia, Iran, Iraq, Kuwait, Libya, Nigeria, Qatar, Saudi Arabia, United Arab Emirates, and Venezuela. Rising world oil demand, tight world oil supplies, and declining U.S. oil and gas production have enabled OPEC to dramatically increase the price of its oil exports since 1973.

ORGANIC COMPOUND - chemical substance containing carbon and hydrogen; other elements, such as nitrogen or oxygen, may also be present.

OVERHEAD - the distillation fraction removed as vapor or liquid from the top of a distillation column, e.g., a pipe still. See distillation.

OXIDATION - the chemical combination of a substance with oxygen. All petroleum products are subject to oxidation, with resultant degradation of their composition and performance. The process is accelerated by heat, light, metal catalysts (e.g., copper), and the presence of water, acids, or solid contaminants. The first reaction products of oxidation are organic peroxides. Continued oxidation, catalyzed by peroxides, forms alcohols, aldehydes, ketones, and organic acids, which can be further oxidized to form high-molecular-weight, oil-insoluble polymers.

OXIDATION STABILITY - resistance of a petroleum product to oxidation; hence, a measure of its potential service or storage life. There are a number of ASTM tests to determine the oxidation stability of a lubricant or fuel, all of which are intended to simulate service conditions on an accelerated basis. In general, the test sample is exposed to oxygen or air at an elevated temperature, and sometimes to water or catalysts (usually iron or copper). Depending on the test, results are expressed in terms of the time required to produce a specified effect (such as a pressure drop), the amount of sludge or gum produced, or the amount of oxygen consumed during a specified period.