Gasoline (American English) or petrol (British English) is a petroleum-derived liquid mixture which is primarily used as a fuel in internal combustion engines. It is also used as a solvent, mainly known for its ability to dilute paints.
It consists mostly of aliphatic hydrocarbons obtained by the fractional distillation of petroleum, enhanced with iso-octane or the aromatic hydrocarbons toluene and benzene to increase its octane rating. Small quantities of various additives are common, for purposes such as tuning engine performance or reducing harmful exhaust emissions. Some mixtures also contain significant quantities of ethanol as a partial alternative fuel.
Most current or former Commonwealth countries use the term petrol, abbreviated from petroleum spirit. In North America, the word gasoline is the common term, where it is often shortened in colloquial usage to simply gas (although petrol is also accepted and used to a lesser extent in Canada). It is not a genuinely gaseous fuel (unlike, for example, liquefied petroleum gas, which is stored under pressure as a liquid, but returned to a gaseous state before combustion). The term petrogasoline is also used. The Jamaican spelling is gasolene.
In aviation, mogas, short for motor gasoline, is used to distinguish automobile fuel from aviation gasoline, or avgas. In British English, gasoline can refer to a different petroleum derivative historically used in lamps, but this usage is relatively uncommon.
Before gasoline was used as fuel for engines, it was sold in small bottles as a treatment against lice and their eggs. This treatment method is no longer common because of the inherent fire hazard and the risk of dermatitis.
In the United States, gasoline was also sold as a cleaning fluid to remove grease stains from clothing. Before dedicated filling stations were established, early motorists bought gasoline in cans to fill their tanks.
During the Franco-Prussian War (1870–71), pétrole was stockpiled in Paris for use against a possible German-Prussian attack on the city. Later in 1871, during the revolutionary Paris Commune, rumours spread around the city of pétroleuses (women using bottles of petrol to commit arson against city buildings).
The name gasoline is similar to that of other petroleum products of the day, most notably petroleum jelly, a highly purified heavy distillate, which was branded Vaseline. The trademark Gasoline was never registered, and eventually became generic.
The word "petrol" was first used in reference to the refined substance in 1892 (it was previously used to refer to unrefined petroleum), and was registered as a trade name by British wholesaler Carless, Capel & Leonard at the suggestion of Frederick Richard Simms. Carless's competitors used the term "motor spirit" until the 1930s.
In many countries gasoline is called Benzine or some variant. The usage derives from the chemical benzene, not from Bertha Benz, who used chemists' shops to purchase the gasoline, a detergent called Ligroin at that time, for her famous drive from Mannheim to Pforzheim and back in 1888, commemorated by the Bertha Benz Memorial Route since 2008. In other countries (Argentina, Uruguay and Paraguay, for example) it's called nafta or some variant.
Gasoline is produced in oil refineries. Material that is separated from crude oil via distillation, called virgin or straight-run gasoline, does not meet the required specifications for modern engines (in particular octane rating; see below), but will form part of the blend.
Many of these hydrocarbons are considered hazardous substances and are regulated in the United States by Occupational Safety and Health Administration. The Material Safety Data Sheet for unleaded gasoline shows at least fifteen hazardous chemicals occurring in various amounts. These include benzene (up to 5% by volume), toluene (up to 35% by volume), naphthalene (up to 1% by volume), trimethylbenzene (up to 7% by volume), MTBE (up to 18% by volume, in some states) and about ten others.
The various refinery streams blended together to make gasoline all have different characteristics. Some important streams are:
(The terms used here are not always the correct terms. They are the jargon normally used in the oil industry. The exact terminology for these streams varies by refinery and by country.)
Overall, a typical gasoline is predominantly a mixture of paraffins (alkanes), naphthenes (cycloalkanes), and olefins (alkenes). The exact ratios can depend on
Currently, many countries set tight limits on gasoline aromatics in general, benzene in particular, and olefin (alkene) content. Such limits result in increasing demand for high octane pure paraffin (alkane) components, such as alkylate, and is forcing refineries to add processing units to reduce the benzene content.
Gasoline can also contain some other organic compounds such as organic ethers (deliberately added), plus small levels of contaminants, in particular sulfur compounds such as disulfides and thiophenes. Some contaminants, in particular thiols and hydrogen sulfide, must be removed because they cause corrosion in engines. Sulfur compounds are usually removed by hydrotreating, yielding hydrogen sulfide, which can then be transformed into elemental sulfur via the Claus process.
The specific density of gasoline ranges from 0.71–0.77, higher densities having a greater volume of aromatics. (0.026 lb/in3; 719.7 kg/m3; 6.073 lb/US gal; 7.29 lb/imp gal). Gasoline floats on water, so water cannot generally be used to extinguish a gasoline fire.
Gasoline is more volatile than diesel oil, Jet-A or kerosene, not only because of the base constituents, but because of the additives that are put into it. The final control of volatility is often achieved by blending with butane. The Reid Vapor Pressure (RVP) test is used to measure the volatility of gasoline. The desired volatility depends on the ambient temperature: in hotter climates, gasoline components of higher molecular weight and thus lower volatility are used. In cold climates, too little volatility results in cars failing to start. In hot climates, excessive volatility results in what is known as "vapor lock" where combustion fails to occur, because the liquid fuel has changed to a gaseous fuel in the fuel lines, rendering the fuel pump ineffective and starving the engine of fuel. (This effect mainly applies to camshaft-driven (engine mounted) fuel pumps that also lack a fuel return line. Vehicles with fuel injection require the fuel to be pressurized, to within a set range. Because camshaft speed is very near zero before the engine is started, an electric pump is used, it is located in the fuel tank so that the fuel may also cool the high pressure pump. Pressure regulation is achieved by returning unused fuel to the tank, thus vapor lock is almost never a problem in a vehicle with fuel injection.)
In the United States, volatility is regulated in large urban centers to reduce the emission of unburned hydrocarbons. In large cities, so-called reformulated gasoline that is less prone to evaporation, among other properties, is required. In Australia, summer petrol volatility limits are set by State Governments and vary between capital cities. Most countries simply have a summer, winter and perhaps intermediate limit.
Volatility standards may be relaxed (allowing more gasoline components into the atmosphere) during emergency anticipated gasoline shortages. For example, on 31 August 2005 in response to Hurricane Katrina, the United States permitted the sale of non-reformulated gasoline in some urban areas, which effectively permitted an early switch from summer to winter-grade gasoline. As mandated by EPA administrator Stephen L. Johnson, this "fuel waiver" was made effective through 15 September 2005.
Besides lowering the volatility of the fuel, other means of controlling the emission of unburned hydrocarbons, for environmental concerns, exist and are used. All vehicles sold in the United States (since at least the 1980s, probably the 1970s or earlier) are required to have a fuel evaporative control system (called an EVAP system in automotive jargon) which collects expanding fuel vapor from the fuel tank in a charcoal-lined canister while the engine is stopped and then releases the collected vapors (through a "purge valve") into the engine intake for burning when the engine is running (usually only after it has reached normal operating temperature.) The fuel evaporative control system is also required to include a gasketed filling cap which seals the fueling inlet to prevent vapors from escaping directly from the tank through it. Modern vehicles with OBD-II emissions control systems will turn on the MIL (Malfunction Indicator Light, a.k.a. "check engine" light) if it is detected that the gas cap is missing or loose and so not sealing. (The general purpose of this light is to indicate when any of the emissions controls are not working properly.)
An important characteristic of gasoline is its octane rating, which is a measure of how resistant gasoline is to the abnormal combustion phenomenon known as pre-detonation (also known as knocking, pinging, spark knock, and other names). Deflagration is the normal type of combustion. Octane rating is measured relative to a mixture of 2,2,4-trimethylpentane (an isomer of octane) and n-heptane. There are a number of different conventions for expressing the octane rating; therefore, the same fuel may be labeled with a different number, depending upon the system used.
During World War II, Germany received much of its oil from Romania. From 2.8 million barrels (450×103 m3) in 1938, Romania’s exports to Germany increased to 13 million barrels (2.1×106 m3) by 1941, a level that was essentially maintained through 1942 and 1943, before dropping by half, due to Allied bombing and mining of the Danube. Although these exports were almost half of Romania’s total production, they were considerably less than what the Germans expected. Even with the addition of the Romanian deliveries, overland oil imports after 1939 could not make up for the loss of overseas shipments. In order to become less dependent on outside sources, the Germans undertook a sizable expansion program of their own meager domestic oil pumping. After 1938, the Austrian oil fields were made available, and the expansion of Nazi crude oil output was chiefly concentrated there. Primarily as a result of this expansion, the Reich's domestic output of crude oil increased from approximately 3.8 million barrels (600×103 m3) in 1938 to almost 12 million barrels (1.9×106 m3) in 1944. Even this was not enough.
Instead, Germany had developed a synthetic fuel capacity that was intended to replace imported or captured oil. Fuels were generated from coal, using either the Bergius process or the Fischer-Tropsch process. Between 1938 and 1943, synthetic fuel output underwent a respectable growth from 10 to 36 million barrels (1.6–5.7×106 m3). The percentage of synthetic fuels compared with the yield from all sources grew from 22% to more than 50% by 1943. The total oil supplies available from all sources for the same period rose from 45 million barrels (7.2×106 m3) in 1938 to 71 million barrels (11.3×106 m3) in 1943.
By the early 1930s, automobile gasoline had an octane rating of 40 and aviation gasoline a rating of 75-80. Aviation gasoline with such high octane numbers could only be refined through a process of distillation of high-grade petroleum. Germany’s domestic oil was not of this quality. Only the additive tetra-ethyl lead could raise the octane to a maximum of 87. The license for the production of this additive was acquired in 1935 from the American holder of the patents, but without high-grade Romanian oil even this additive was not very effective. 100 octane fuel, designated either 'C-2' (natural) or 'C-3' (synthethic) was introduced in late 1939 with the Daimler-Benz DB 601N engine, used in certain of the Luftwaffe`s Bf 109E and Bf 109F single-engined fighters, Bf 110C twin-engined fighters, and several bomber types. Some later combat types, most notably the BMW 801D-powered Fw 190A, F and G series, and later war Bf 109G and K models, used C-3 as well. The nominally 87 octane aviation fuel designated 'B-4' was produced in parallel during the war.
In the United States the oil was not "as good", and the oil industry had to invest heavily in various expensive boosting systems. This turned out to have benefits: the US industry started delivering fuels of increasing octane ratings by adding more of the boosting agents, and the infrastructure was in place for a post-war octane-agents additive industry. Good crude oil was no longer a factor during wartime, and by war's end American aviation fuel was commonly 130 octane, and 150 octane was available in limited quantities for fighters from mid-1944. This high octane could easily be used in existing engines to deliver much more power by increasing the pressure delivered by the superchargers.
In late 1942, the Germans increased the octane rating of their high-grade 'C-3' aviation fuel to 150 octane. The relative volumes of production of the two grades B-4 and C-3 cannot be accurately given, but in the last war years perhaps two-thirds of the total was C-3. Every effort was being made toward the end of the war to increase isoparaffin production; more isoparaffin meant more C-3 available for fighter plane use.
A common misconception exists concerning wartime fuel octane numbers. There are two octane numbers for each fuel, one for lean mix and one for rich mix, rich being greater. The misunderstanding that German fuels had a lower octane number (and thus a poorer quality) arose because the Germans quoted the lean mix octane number for their fuels while the Allies quoted the rich mix number. Standard German high-grade 'C-3' aviation fuel used in the later part of the war had lean/rich octane numbers of 100/130. The Germans listed this as a 100 octane fuel, the Allies as 130 octane.
After the war the US Navy sent a Technical Mission to Germany to interview German petrochemists and examine German fuel quality. Their report entitled “Technical Report 145-45 Manufacture of Aviation Gasoline in Germany” chemically analyzed the different fuels, and concluded that “Toward the end of the war the quality of fuel being used by the German fighter planes was quite similar to that being used by the Allies.”
Gasoline contains about 32.0 MJ/L (8.89 kW·h/L, 132 MJ/US gal, 36.6 kWh/US gal) or 12.9 kWh/kg in comparison to batteries. This is an average; gasoline blends differ, and therefore actual energy content varies from season to season and from batch to batch, by up to 4% more or less than the average, according to the US EPA. On average, about 19.5 US gallons (16.2 imp gal; 74 L) of gasoline are available from a 42-US-gallon (35 imp gal; 160 L) barrel of crude oil (about 46% by volume), varying due to quality of crude and grade of gasoline. The remaining residue comes off as products ranging from tar to naptha.
|87 Octane Gasoline/Petrol||32.0||44.4||150,100||125,000||Min 91|
|Autogas (LPG) (60% Propane + 40% Butane)||26.8||46||108|
|Gasohol (10% ethanol + 90% gasoline)||31.2||145,200||120,900||93/94|
|Aviation gasoline (high octane gasoline, not jet fuel)||33.5||46.8||144,400||120,200|
|Jet fuel (kerosene based)||35.1||43.8||151,242||125,935|
|Liquefied natural gas||25.3||55||109,000||90,800|
|Hydrogen||10.1 (at 20 kelvins)||142||130|
(*) Diesel fuel is not used in a gasoline engine, so its low octane rating is not an issue; the relevant metric for diesel engines is the cetane number
A high octane fuel such as liquefied petroleum gas (LPG) has a lower energy content than lower octane gasoline, resulting in an overall lower power output at the regular compression ratio an engine ran at on gasoline. However, with an engine tuned to the use of LPG (i.e. via higher compression ratios such as 12:1 instead of 8:1), this lower power output can be overcome. This is because higher-octane fuels allow for a higher compression ratio—this means less space in a cylinder on its combustion stroke, hence a higher cylinder temperature which improves efficiency according to Carnot's theorem, along with fewer wasted hydrocarbons (therefore less pollution and wasted energy), bringing higher power levels coupled with less pollution overall because of the greater efficiency.
The main reason for the lower energy content (per litre) of LPG in comparison to gasoline is that it has a lower density. Energy content per kilogram is higher than for gasoline (higher hydrogen to carbon ratio). The weight-density of gasoline is about 740 kg/m³ (6.175 lb/US gal; 7.416 lb/imp gal).
Different countries have some variation in what RON (Research Octane Number) is standard for gasoline, or petrol. In the UK, ordinary regular unleaded petrol is 91 RON (not commonly available), premium unleaded petrol is always 95 RON, and super unleaded is usually 97-98 RON. However both Shell and BP produce fuel at 102 RON for cars with hi-performance engines, and the supermarket chain Tesco began in 2006 to sell super unleaded petrol rated at 99 RON. In the US, octane ratings in unleaded fuels can vary between 86-87 AKI (91-92 RON) for regular, through 89-90 AKI (94-95 RON) for mid-grade (European Premium), up to 90-94 AKI (95-99 RON) for premium (European Super). ????
The mixture known as gasoline, when used in high compression internal combustion engines, has a tendency to autoignite (detonation) causing a damaging "engine knocking" (also called "pinging" or "pinking") noise. Early research into this effect was led by A.H. Gibson and Harry Ricardo in England and Thomas Midgley and Thomas Boyd in the United States. The discovery that lead additives modified this behavior led to the widespread adoption of their use in the 1920s and therefore more powerful higher compression engines. The most popular additive was tetra-ethyl lead. However, with the discovery of the environmental and health damage caused by the lead, and the incompatibility of lead with catalytic converters found on virtually all newly sold US automobiles since 1975, this practice began to wane (encouraged by many governments introducing differential tax rates) in the 1980s. Most countries are phasing out leaded fuel; different additives have replaced the lead compounds. The most popular additives include aromatic hydrocarbons, ethers and alcohol (usually ethanol or methanol). In the US, where lead had been blended with gasoline (primarily to boost octane levels) since the early 1920s, standards to phase out leaded gasoline were first implemented in 1973 - due in great part to studies conducted by Philip J. Landrigan. In 1995, leaded fuel accounted for only 0.6% of total gasoline sales and less than 2000 short tons (1814 t) of lead per year. From 1 January 1996, the Clean Air Act banned the sale of leaded fuel for use in on-road vehicles. Possession and use of leaded gasoline in a regular on-road vehicle now carries a maximum $10,000 fine in the US. However, fuel containing lead may continue to be sold for off-road uses, including aircraft, racing cars, farm equipment, and marine engines. The ban on leaded gasoline led to thousands of tons of lead not being released into the air by automobiles. Similar bans in other countries have resulted in lowering levels of lead in people's bloodstreams.
A side effect of the lead additives was protection of the valve seats from erosion. Many classic cars' engines have needed modification to use lead-free fuels since leaded fuels became unavailable. However, "Lead substitute" products are also produced and can sometimes be found at auto parts stores. These were scientifically tested and some were approved by the Federation of British Historic Vehicle Clubs at the UK's Motor Industry Research Association (MIRA) in 1999.
In some parts of South America, Asia, Eastern Europe and the Middle East, leaded gasoline is still in use. Leaded gasoline was phased out in sub-Saharan Africa effective 1 January 2006. A growing number of countries have drawn up plans to ban leaded gasoline in the near future. However, in Britain there is now a growing market for using Four Star leaded petrol in classic cars and motorcycles because of detonation and valve seat erosion. A sole petroleum wholesaler, the Bayford Group, is EU-licenced to distribute the leaded fuel and it is sold at select outlets around the UK. Not all counties are covered and the fuel costs approximately twice that of unleaded petrol.
Methylcyclopentadienyl manganese tricarbonyl (MMT) has been used for many years in Canada and recently in Australia to boost octane. It also helps old cars designed for leaded fuel run on unleaded fuel without need for additives to prevent valve problems.
US Federal sources state that MMT is suspected to be a powerful neurotoxin and respiratory toxin, and a large Canadian study concluded that MMT impairs the effectiveness of automobile emission controls and increases pollution from motor vehicles.
In 1977 use of MMT was banned in the US by the Clean Air Act until the Ethyl Corporation could prove that the additive would not lead to failure of new car emissions-control systems. As a result of this ruling, the Ethyl Corporation began a legal battle with the EPA, presenting evidence that MMT was harmless to automobile emissions-control systems. In 1995 the US Court of Appeals ruled that the EPA had exceeded its authority, and MMT became a legal fuel additive in the US. MMT is nowadays manufactured by the Afton Chemical Corporation division of Newmarket Corporation.
In the United States, ethanol is sometimes added to gasoline but sold without an indication that it is a component.
In several states, ethanol is added by law to a minimum level which is currently 5.9%. Most fuel pumps display a sticker stating that the fuel may contain up to 10% ethanol, an intentional disparity which allows the minimum level to be raised over time without requiring modification of the literature/labelling. The bill which was being debated at the time the disclosure of the presence of ethanol in the fuel was mandated has recently passed.
In the EU, 5% ethanol can be added within the common gasoline spec (EN 228). Discussions are ongoing to allow 10% blending of ethanol. Most gasoline sold in Sweden has 5% ethanol added.
In Brazil, the Brazilian National Agency of Petroleum, Natural Gas and Biofuels (ANP) requires that gasoline for automobile use has 25% of ethanol added to its composition.
In the United States the most commonly used aircraft gasoline, avgas, or aviation gas, is known as 100LL (100 octane, low lead) and is dyed blue. Red dye has been used for identifying untaxed (non-highway use) agricultural diesel. The UK uses red dye to differentiate between regular diesel fuel, (often referred to as DERV from Diesel-Engined Road Vehicle), which is undyed, and diesel intended for agricultural and construction vehicles like excavators and bulldozers. Red diesel is still occasionally used on HGVs which use a separate engine to power a loader crane. This is a declining practice however, as many loader cranes are powered directly by the tractor unit.
Oxygenate blending adds oxygen to the fuel in oxygen-bearing compounds such as MTBE, ETBE and ethanol, and so reduces the amount of carbon monoxide and unburned fuel in the exhaust gas, thus reducing smog. In many areas throughout the US oxygenate blending is mandated by EPA regulations to reduce smog and other airborne pollutants. For example, in Southern California, fuel must contain 2% oxygen by weight, resulting in a mixture of 5.6% ethanol in gasoline. The resulting fuel is often known as reformulated gasoline (RFG) or oxygenated gasoline. The federal requirement that RFG contain oxygen was dropped 6 May 2006 because the industry had developed VOC-controlled RFG that did not need additional oxygen.
MTBE use is being phased out in some states due to issues with contamination of ground water. In some places, such as California, it is already banned. Ethanol and to a lesser extent the ethanol derived ETBE are common replacements. Since most ethanol is derived from biomatter such as corn, sugar cane or grain, it is referred to as bio-ethanol. A common ethanol-gasoline mix of 10% ethanol mixed with gasoline is called gasohol or E10, and an ethanol-gasoline mix of 85% ethanol mixed with gasoline is called E85. The most extensive use of ethanol takes place in Brazil, where the ethanol is derived from sugarcane. In 2004, over 3.4 billion US gallons (2.8 billion imp gal/13 million m³) of ethanol was produced in the United States for fuel use, mostly from corn, and E85 is slowly becoming available in much of the United States, though many of the relatively few stations vending E85 are not open to the general public. The use of bioethanol, either directly or indirectly by conversion of such ethanol to bio-ETBE, is encouraged by the European Union Directive on the Promotion of the use of biofuels and other renewable fuels for transport. However since producing bio-ethanol from fermented sugars and starches involves distillation, ordinary people in much of Europe cannot legally ferment and distill their own bio-ethanol at present (unlike in the US where getting a BATF distillation permit has been easy since the 1973 oil crisis.)
Gasoline, as delivered at the pump, also contains additives to reduce internal engine carbon buildups, improve combustion, and to allow easier starting in cold climates.
Many of the non-aliphatic hydrocarbons naturally present in gasoline (especially aromatic ones like benzene), as well as many anti-knocking additives, are carcinogenic. Because of this, any large-scale or ongoing leaks of gasoline pose a threat to the public's health and the environment, should the gasoline reach a public supply of drinking water. The chief risks of such leaks come not from vehicles, but from gasoline delivery truck accidents and leaks from storage tanks. Because of this risk, most (underground) storage tanks now have extensive measures in place to detect and prevent any such leaks, such as sacrificial anodes. Gasoline is rather volatile (meaning it readily evaporates), requiring that storage tanks on land and in vehicles be properly sealed. The high volatility also means that it will easily ignite in hot weather conditions, unlike diesel for example. Appropriate venting is needed to ensure the level of pressure is similar on the inside and outside. Gasoline also reacts dangerously with certain common chemicals.
Gasoline is also one of the sources of pollutant gases. Even gasoline which does not contain lead or sulfur compounds produces carbon dioxide, nitrogen oxides, and carbon monoxide in the exhaust of the engine which is running on it. Furthermore, unburnt gasoline and evaporation from the tank, when in the atmosphere, react in sunlight to produce photochemical smog. Addition of ethanol increases the volatility of gasoline.
Through misuse as an inhalant, gasoline also contributes to damage to health. Petrol sniffing is a common way of obtaining a high for many people and has become epidemic in some poorer communities and indigenous groups in America, Australia, Canada, New Zealand and some Pacific Islands. In response, Opal fuel has been developed by the BP Kwinana Refinery in Australia, and contains only 5% aromatics (unlike the usual 25%) which inhibits the effects of inhalation.
Like other alkanes, gasoline burns in the vapor phase and, coupled with its volatility, this makes leaks highly dangerous when sources of ignition are present. Many accidents involve gasoline being used in an attempt to light bonfires; rather than helping the material on the bonfire to burn, some of the gasoline vaporises quickly after being poured and mixes with the surrounding air, so when the fire is lit a moment later the vapor surrounding the bonfire instantly ignites in a large fireball, engulfing the unwary user. The vapor is also heavier than air and tends to collect in garage inspection pits.
The US accounts for about 44% of the world’s gasoline consumption. In 2003 The US consumed 476.474 gigalitres (1.25871×1011 US gal; 1.04810×1011 imp gal), which equates to 1.3 gigalitres of gasoline each day (about 360 million US or 300 million imperial gallons). The US used about 510 billion litres (138 billion US gal/115 billion imp gal) of gasoline in 2006, of which 5.6% was mid-grade and 9.5% was premium grade.
Western countries have among the highest usage rates per person.
Because a greater proportion of the price of gasoline in the United States is due to the cost of oil, rather than taxes, the price of the retail product is subject to greater fluctuations (vs. outside the US) when calculated as a percentage of cost-per-unit, but is less variable in absolute terms. From 1998 to 2004 the price of gasoline was between $1 to $2 USD per U.S. gallon. After 2004, the price increased until the average gas price reached a high of $4.11 per U.S. gallon in mid-2008, but has receded to approximately $2.60 per U.S. gallon as of September 2009.
Unlike other goods in the United States, gasoline is sold with tax included. Taxes are added by federal, state and local governments. As of 2009, the federal tax is 18.4¢ per gallon for gasoline and 24.4¢ per gallon for diesel (excluding Red diesel). Among states, the highest gasoline tax rates, including the federal taxes as of 2005, are New York (62.9¢/gal), Hawaii (60.1¢/gal), & California (60¢/gal). However, many states' taxes are a percentage and thus vary in amount depending on the cost of the gasoline.
About 9 percent of all gasoline sold in the US in May 2009 was premium gas, according to the Energy Information Administration. Consumer Reports magazine says “If your car can run on regular, run it on regular.” The Associated Press said that premium gas—which is a higher octane and costs several cents a gallon more than regular unleaded-should be used only if the manufacturer says it is “required.” 
Good quality gasoline should be stable almost indefinitely if stored properly. Such storage should be in an airtight container, to prevent oxidation or water vapors mixing, and at a stable cool temperature, to reduce the chance of the container leaking. When gasoline is not stored correctly and is left for a period of time, gums and varnishes may build up and precipitate in the gasoline, causing "stale fuel". This may cause gums to build up in the fuel tank, lines, and carburetor or fuel injection components making it harder to start the engine. However upon the resumption of regular vehicle usage, the buildups should eventually be cleaned up by the flow of fresh petrol. A fuel stabilizer may be used to extend the life of the fuel that is not or can not be stored properly. Fuel stabilizer is commonly used for small engines such as lawnmower and tractor engines to promote quicker and more reliable starting. Users have been advised to keep gasoline containers and tanks more than half full and properly capped to reduce air exposure, to avoid storage at high temperatures, to run an engine for ten minutes to circulate the stabilizer through all components prior to storage, and to run the engine at intervals to purge stale fuel from the carburetor.
Gummy, sticky resin deposits result from oxidative degradation of gasoline. This degradation can be prevented through the use of antioxidants such as phenylenediamines, alkylenediamines (diethylenetriamine, triethylenetetramine, etc), and alkylamines (diethylamine, tributylamine, ethylamine). Other useful additives include gum inhibitors such as N-substituted alkylaminophenols and colour stabilizers such as N-(2-aminoethyl)piperazine, N,N-diethylhydroxylamine, and triethylenetetramine.
Improvements in refinery techniques have generally reduced the reliance on the catalytically or thermally cracked stocks most susceptible to oxidation. Gasoline containing acidic contaminants such as naphthenic acids can be addressed with additives including strongly basic organo-amines such as N,N-diethylhydroxylamine, preventing metal corrosion and breakdown of other antioxidant additives due to acidity. Hydrocarbons with a bromine number of 10 or above can be protected with the combination of unhindered or partially hindered phenols and oil soluble strong amine bases such as monoethanolamine, N-(2-aminoethyl)piperazine, cyclohexylamine, 1,3-cyclohexane-bis(methylamine), 2,5-dimethylaniline, 2,6-dimethylaniline, diethylenetriamine and triethylenetetramine.
Many of these alternatives are less damaging to the environment than gasoline, but the first generation biofuels are still not 100 percent clean.