question: What does the number like 89 or 91 then Octane mean for cars and why does the higher number = more expense?
comment: Ill make this short and simple. The higher the number the more resistant the gas is to ignite before spark ignition. If the octane is too low for the particular engine the gas will ignite and explode before the spark ignition and that is called detonation or pre-igniton and can destroy an engine. Engine's have compression ratios, the higher the compression ratio the more power that can be made, BUT that also requires a higher octane fuel so it does not cause pre-ignition. Generally speaking normal commuter and economy cars will run on the lower 87 octane, while performance cars will require the high octane 91+.
passages: BULLET::::- Denmark: 95 RON is a common choice, with 92 and 95 being widely available. However several fuel stations are phasing out 92 RON. By law, it is decided that all gasoline companies from July 2010 should use a mix containing 5% bioethanol in the gasoline.
  
  BULLET::::- Ecuador: "Extra" with 87 and "Super" with 92 (RON) are available in all fuel stations. "Extra" is the most commonly used. All fuels are unleaded.
   Section::::Measurement methods.:Aviation gasoline octane ratings.
   BULLET::::- Egypt: Egyptian fuel stations had 90 RON until July 2014 when the government found no remaining use for it, leaving only 92 RON and 95 RON. 80 RON is found in a very limited amount of fuel stations as they are used only for extremely old cars that cannot cope with high octane fuel. 95 RON was used limitedly due to its high price (more than twice the price of 92 RON). But after the increasing the prices again in 2018ref
   The selection of octane ratings available at the pump can vary greatly from region to region.
   That practice can be fine for "cruising" straight and level and in smooth air, but in case of the need to rapidly add power (sudden climb, headwind, etc), the additional "insurance policy" of excess octane in avgas helps prevent dangerously lean fuel-air mixtures from rapidly melting and physically "burning" the aluminum pistons in an air-cooled aircraft engine. With only fuel, lubricating oil and airflow to cool the engine and a "lean of peak" mixture with no "excess" fuel for cooling, the engine is only a few seconds of dangerously lean mixtures, autoignition and detonation away from catastrophic failure.
  
  Section::::Regional variations.
   BULLET::::- China: 92 and 95 (RON) (previously 93 and 97) are commonly offered. In limited areas higher rating such as 98 RON is available. In some rural areas it can be difficult to find fuel with over 92 RON.
  
  BULLET::::- Chile: 93, 95 and 97 RON are standard at almost all gas stations thorough Chile. The three types are unleaded.
  
  BULLET::::- Colombia: "Ecopetrol", Colombia's monopoly of refining and distribution of gasoline establishes a minimum AKI of 81 octanes for "Corriente" gasoline and minimum AKI of 87 octanes for "Extra" gasoline. (91.5 RON corriente, and 91 RON for extra)
   The other rarely-discussed reality with high-octane fuels associated with "high performance" is that as octane increases, the specific gravity and energy content of the fuel per unit of weight are reduced. The net result is that to make a given amount of power, more high-octane fuel must be burned in the engine. Lighter and "thinner" fuel also has a lower specific heat, so the practice of running an engine "rich" to use excess fuel to aid in cooling requires richer and richer mixtures as octane increases.
   BULLET::::- Bahrain: 91 and 95 (RON), standard in all gasoline stations in the country and advertised as (Jayyid) for Regular or 91 and (Mumtaz) for Premium or 95 and 98 (RON) as super.
   Section::::Measurement methods.:Anti-Knock Index (AKI) or (R+M)/2.
  
  In most countries in Europe (also in Australia, Pakistan and New Zealand) the "headline" octane rating shown on the pump is the RON, but in Canada, the United States, Brazil, and some other countries, the headline number is the simple mean or average of the RON and the MON, called the Anti-Knock Index (AKI), and often written on pumps as (R+M)/2. It may also sometimes be called the Posted Octane Number (PON).
  
  Section::::Measurement methods.:Difference between RON, MON, and AKI.
   Section::::Octane.
  
  In Australia, gasoline is unleaded, and available in 91, 95, 98 and 100 octane (names of various petrols differ from brand to brand). Fuel additives for use in cars designed for leaded fuel are available at most filling stations.
  
  In Canada, the most commonly found octane grades are 87 (regular), 89 (mid grade) and 91 (premium), using the same "(R+M)/2 Method" used in the U.S. (see below).
   Aviation gasolines used in piston aircraft engines common in general aviation have a slightly different method of measuring the octane of the fuel. Similar to an AKI, it has two different ratings, although it is referred to only by the lower of the two. One is referred to as the "aviation lean" rating and is the same as the MON of the fuel up to 100. The second is the "aviation rich" rating and corresponds to the octane rating of a test engine under forced induction operation common in high-performance and military piston aircraft. This utilizes a supercharger, and uses a significantly richer fuel/air ratio for improved detonation resistance. 
   Because of the high cost of unleaded, high-octane avgas, and the tendency of piston-engine aircraft to be recreational vehicles and the potential for fuel loss via evaporation/theft/leaks, most general aviation pilots attempt to save money by tuning their fuel-air mixtures and ignition timing to run "lean of peak". 
   In the United States all motor vehicle gasoline is unleaded and is available in several grades with different octane rating; 87 (Regular), 89 (Mid-Grade), and 93 (Premium) are typical grades. The maximum octane rating in California is generally 91. At high altitudes in the Mountain States and the Black Hills of South Dakota, regular unleaded can be as low as 85 octane; this practice is now increasingly controversial, since it was instituted when most cars had carburetors instead of the fuel injection and electronic engine controls standard in recent decades.
   Another type of octane rating, called Motor Octane Number (MON), is determined at 900 rpm engine speed instead of the 600 rpm for RON. MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern pump gasoline will be about 8 to 12 octane lower than the RON, but there is no direct link between RON and MON. Pump gasoline specifications typically require both a minimum RON and a minimum MON.
   "Octane" is colloquially used as a short form of "octane rating" (an index of a fuel's ability to resist engine knock at high compression, which is a characteristic of octane's branched-chain isomers, especially iso-octane), particularly in the expression "high octane". 
   Octanes are a family of hydrocarbons that are typical components of gasoline. They are colorless liquids that boil around 125 °C (260 °F). One member of the octane family, isooctane, is used as a reference standard to benchmark the tendency of gasoline or LPG fuels to resist self-ignition.
   The most common type of octane rating worldwide is the Research Octane Number (RON). RON is determined by running the fuel in a test engine with a variable compression ratio under controlled conditions, and comparing the results with those for mixtures of iso-octane and n-heptane.
  
  Section::::Measurement methods.:Motor Octane Number (MON).
   BULLET::::- Costa Rica: RECOPE, Costa Rica's distribution monopoly, establishes the following ratings: Plus 91 (at least 91 RON) and Super (at least 95 RON).
  
  BULLET::::- Croatia: All fuel stations offer unleaded "Eurosuper BS" (abbreviation "BS" meaning "no sulfur content") 95 RON fuel, many also offer "Eurosuper Plus BS" 98 RON. Some companies offer 100 RON fuel instead of 98.
  
  BULLET::::- Cyprus: All fuel stations offer unleaded 95 and 98 RON and a few offer 100 RON as well.
   Another type of octane rating, called Observed Road Octane Number (RdON), is derived from testing gasolines in real world multi-cylinder engines, normally at wide open throttle. It was developed in the 1920s and is still reliable today. The original testing was done in cars on the road but as technology developed the testing was moved to chassis dynamometers with environmental controls to improve consistency.
  
  Section::::Measurement methods.:Octane Index.
   The most commonly used current fuel, 100LL, has an aviation lean rating of 100 octane, and an aviation rich rating of 130.
  
  Section::::Examples.
  
  The RON/MON values of n-heptane and iso-octane are exactly 0 and 100, respectively, by the definition of octane rating. The following table lists octane ratings for various other fuels.
  
  Section::::Effects.
  
  Higher octane ratings correlate to higher activation energies: the amount of applied energy required to initiate combustion. Since higher octane fuels have higher activation energy requirements, it is less likely that a given compression will cause uncontrolled ignition, otherwise known as autoignition or detonation.
   Catalytic cracking, coking and other such conversion units are referred to toas secondary processing units. The Nelson Complexity Index, captures the proportion of the secondary conversion unit capacities relative to the primary distillation or topping capacity. The Nelson Complexity Index typically varies from about 2 for hydroskimming refineries, to about 5 for the Cracking refineries and over 9 for the Coking refineries.
   Any mixture greater than 14.7:1 is considered a lean mixture; any less than 14.7:1 is a rich mixture – given perfect (ideal) "test" fuel (gasoline consisting of solely "n"-heptane and iso-octane). In reality, most fuels consist of a combination of heptane, octane, a handful of other alkanes, plus additives including detergents, and possibly oxygenators such as MTBE (methyl tert-butyl ether) or ethanol/methanol. These compounds all alter the stoichiometric ratio, with most of the additives pushing the ratio downward (oxygenators bring extra oxygen to the combustion event in liquid form that is released at time of combustions; for MTBE-laden fuel, a stoichiometric ratio can be as low as 14.1:1). Vehicles that use an oxygen sensor or other feedback loop to control fuel to air ratio (lambda control), compensate automatically for this change in the fuel's stoichiometric rate by measuring the exhaust gas composition and controlling fuel volume. Vehicles without such controls (such as most motorcycles until recently, and cars predating the mid-1980s) may have difficulties running certain fuel blends (especially winter fuels used in some areas) and may require different jets (or otherwise have the fueling ratios altered) to compensate. Vehicles that use oxygen sensors can monitor the air–fuel ratio with an air–fuel ratio meter.
   The octane rating of gasoline is measured in a test engine and is defined by comparison with the mixture of 2,2,4-trimethylpentane (iso-octane) and heptane that would have the same anti-knocking capacity as the fuel under test: the percentage, by volume, of 2,2,4-trimethylpentane in that mixture is the octane number of the fuel. For example, gasoline with the same knocking characteristics as a mixture of 90% iso-octane and 10% heptane would have an octane rating of 90. A rating of 90 does not mean that the gasoline contains just iso-octane and heptane in these proportions but that it has the same detonation resistance properties (generally, gasoline sold for common use never consists solely of iso-octane and heptane; it is a mixture of many hydrocarbons and often other additives). Because some fuels are more knock-resistant than pure iso-octane, the definition has been extended to allow for octane numbers greater than 100.
   Section::::Types.:Dealing with customer characteristics.:Employee discount.
  
  A discount offered by a company to employees who buy its products.
  
  In 2005, the American automakers ran an "employee discount" for all customers promotional campaign in order to entice buyers, with some success.
  
  Section::::Types.:Dealing with customer characteristics.:Military discount.
   Because of the 8 to 12 octane number difference between RON and MON noted above, the AKI shown in Canada and the United States is 4 to 6 octane numbers lower than elsewhere in the world for the same fuel. This difference between RON and MON is known as the fuel's Sensitivity, and is not typically published for those countries that use the Anti-Knock Index labelling system.
  
  See the table in the following section for a comparison.
  
  Section::::Measurement methods.:Observed Road Octane Number (RdON).
  