Initially developed for the severe environment found in gas turbine or jet engines, synthetic oils create stable, predictable and desirable lubrication as a result of their uniformity. When compared to mineral-based oils, among other attributes, synthetic lubricants exhibit superior oxidative and thermal stability. In other words, when exposed to high temperatures, they resist oxidation (a mixture with and reaction to air) and deterioration. Synthetic oils also possess a high viscosity index (VI), which means their viscosity changes very little from a cold start-up to hot operating conditions (i.e., they flow better when cold, yet maintain excellent lubricating ability when hot). In broad terms, the higher VI equates to less wear and better fuel economy.