The idea of ​​the hybrid electric vehicle (HEV) has been around for more than a decade, as many people may not have initially thought. In fact, hybrid vehicles were developed in the last century. The combination of an electric motor and a petrol engine has thrilled the minds of scientists and inventors for many years. Hybrid cars have surpassed many feats as they progressed over the years, such as increasing fuel consumption and reducing pollutants expelled by regular internal combustion engines. Although the hybrid car is currently in high demand, some people believe that these cars are just a quick fix before bigger and better ideas, such as fuel cell vehicles, begin to take over the automotive industry. However, the development of the hybrid car has had many effects on today's society and may continue to have them in the future. When the 1970s came and the oil crisis hit, gas prices increased enormously and people were very worried about the dependence on oil and once again the idea of ​​hybrid cars came up. The main financial support has come from the US Department of Energy, but some automotive companies have also invested money. At the beginning of the 1990s, Volkswagen was the only car manufacturer to consider marketing a hybrid vehicle, but only in Europe. 1993 kicked off a major event in the advancement of hybrid cars. The Department of Energy signed a five-year, $138 million development agreement with General Motors and a $122 million agreement with Ford to design and build pre-production hybrid prototypes that could be commercialized in less than 10 years. Four years later a new generation of hybrid vehicles was created with the introduction of the Toyota Prius (Sperling, p. 101). Today's hybrids come in many different varieties, such as light or full and in series or parallel. Mild hybrids require the use of an electric motor to assist the gas engine when more power is needed. It can only move from the stopped position if the internal combustion engine is engaged. The Mild Hybrid can be divided into 3 subsystems. The Start/Stop system, also called micro hybrid, turns off the engine when the car normally idles and restarts it instantly when pressure is applied to the accelerator. This type of system increases fuel efficiency by only about 10% and is the most basic of all hybrid vehicles.