The environmental benefits of fuel ethers can be divided into two main categories. There are so-called "direct" effects, mainly due to more complete fuel combustion (as a result of organic oxygen presence) and "indirect" ones, coming from the dilution of other, less desirable, gasoline pool components. It is also important to note that their use reduces emissions from all types of gasoline vehicles, regardless of their emission-control technology. Although it seems to be of less importance for EURO IV standard cars with newest catalyst techniques, fuel ethers help to improve combustion for these cars especially in the cold starting phase of the engine, when the catalytic converter is not working.

Direct effects include the reduction of both "regulated" and "unregulated" emissions. Among the specific pollutants already limited by law are carbon monoxide (CO) as well as unburned hydrocarbons (HCs).The second category includes those pollutants that have recently been the focus of attention for the EU authorities, even though they are not yet the subject of legislation. Probably the most important are particulate matter (PM) and ground-level ozone.

Indirect effects lead to reduction of sulphur, olefins, aromatics and benzene levels, regardless of whether the fuel is used in current or older technology vehicles.

The magnitude of the beneficial effects does depend on a number of parameters, such as the percentage of MTBE actually blended in the petrol, the presence of after-burning catalyst devices, the type and age of the engine or the driving cycle. Nevertheless, there is general agreement in the industrial and scientific community on broad values.

Reducing exhaust emissions of carbon monoxide: CO poisoning occurs because haemoglobin (the protein in our blood that carries oxygen) absorbs CO 200 times faster than it can absorb oxygen. This can produce many symptoms including headaches, fatigue, nausea, dizziness, confusion and irritability. Continued exposure can lead to vomiting, brain damage, heart irregularity, breathing difficulties and muscle weakness. Absorption at concentrations as low as 800 ppm can cause unconsciousness in less than an hour and death in only 2-3 hours. CO also makes a significant contribution to ground-level ozone.

Carbon monoxide results from incomplete burning of fuel. Adding oxygen to gasoline results in more efficient and complete fuel combustion, which in turn leads to significant decreases in CO emissions, in the same range as the percentage of fuel ether content in the gasoline.

Unburned hydrocarbons: HCs coming out of vehicle exhaust pipes unburned (or partially burned and transformed into other chemicals) fall into the category of VOCs (Volatile Organic Compounds), which have for many years been the focus of legislative attention in Europe and worldwide. HCs' adverse effects on human health have been widely reported.

Since most emissions of unburned HCs occur in the period before catalyst warm-up, this problem is not alleviated by improved vehicle technology. Conservatively, for each 1 or 2% of fuel ether, there is a 1% reduction in total HC emissions.

Particulate matter: PM, although not currently included in European legislation, is gaining continuously in importance. In numerous diesel particulates it has been shown that particulate extracts are mutagenic. Some data suggests that particles emitted from gasoline-fuelled cars may be smaller in size and thus may penetrate the lungs more easily than diesel particles.

Although there is very little data available on gasoline particulates, and a common agreement has not yet been reached on any system of measurement, a recent study (SAE 2001 01 2017) estimates that each 1% of fuel ether results in a 2 to 3% PM emission reduction.

Ozone: O3, the main ingredient of smog, poses a serious air quality problem in many parts of Europe. Even at low levels, ozone can cause a number of adverse respiratory effects. It can irritate the respiratory system, reduce lung function, aggravate asthma, inflame and damage lung cells, aggravate chronic lung diseases and may cause permanent lung damage. O3 also affects the natural environment: it compromises plants' growth and reproduction, it makes them more susceptible to disease and reduces agricultural yields for many economically important crops.

Fuel ethers, by reducing direct VOCs' Ozone Forming Potential (OFP), performs significantly better than other octane blending components. It generates about half of the ozone when compared to iso/alkylates and one-tenth that of aromatics.

Aromatics: Blending fuel ethers into petrol allows, by dilution, a consequential reduction of the level of benzene and aromatics components.

It is estimated that, for each 1% of MTBE, there is an equivalent percentage reduction in benzene emissions, both evaporative and exhaust.

Lead: As lead is a toxic compound, leaded gasoline is phased out on most areas of the world, including Europe. Fuel ethers have been widely used all over the world for over 20 years as a safe and clean "octane enhancer", substituting lead.

"Knock-on" effects and "backsliding risk": Last but not least, it should be noted that by using fuel ethers, refiners actually produce gasoline with environmental qualities better than those required by legislation, such as reduced volatility and exhaust emission properties that exceed regulations. Without fuel oxygenates, real world air quality could easily worsen. High olefins concentration is just one example. To produce fuel ethers, refiners convert C4 olefins, making good environmental use of that reactive components, which would otherwise have to be converted into gasoline blending components with much less positive effects in terms of octane value and exhaust emission reduction, compared to MTBE and ETBE.