E5

E5 is a petrol fuel that contains 5% ethanol by volume and 95% mineral gasoline. It is the standard unleaded petrol in most European markets and has been the baseline automotive fuel for decades. The ethanol component is typically derived from fermented grain or sugar crops and serves as an octane booster and emissions reducer.

The ethanol in E5 increases fuel octane rating by approximately one to two points, allowing engines to run without knocking at higher compression ratios. It also reduces carbon monoxide and particulate emissions during combustion. However, ethanol is hygroscopic, meaning it absorbs water from the air. This property matters for fuel stability: E5 can hold a maximum of around 0.5% water by volume before phase separation occurs, where ethanol and water drop out of solution below the other fuel.

E5 is compatible with all petrol engines manufactured since the 1980s and with nearly all vehicles on the road today. Older carburetted engines and fuel systems made before the widespread adoption of ethanol blends may experience rubber hose degradation or fuel system corrosion over extended storage, though this is rare with E5's low ethanol content. Some classic or vintage vehicles require E0 (pure mineral petrol) or require fuel system inspection before use.

E5 remains the standard grade at most fuel pumps across Europe, though E10 (10% ethanol) is increasingly available and mandated in some regions. E5 is chosen for its broad compatibility, established supply chains, and minimal engine modification requirements. The naming convention reflects ethanol percentage directly: E0, E5, E10, E20, and E85 designate 0%, 5%, 10%, 20%, and 85% ethanol respectively.

Fuel quality standards for E5 are governed by EN 228 in Europe. The standard specifies volatility, distillation range, corrosion properties, and thermal stability to ensure performance across climates and seasons. Storage stability is important for fuel delivered to pumps months after refining; oxidation and gum formation increase if fuel sits in warm conditions or is exposed to light and air.