Just because it's difficult to predict the future doesn't mean people won't try. See, for example, the CEO of Shell, who said last week that he expects plug-in vehicles to make up 40 percent of the new car market in 2050. The U.S. Energy Information Administration isn't looking that far ahead with its latest prediction – and it isn't trying to convince stockholders of one thing or another – but it sees "alternative vehicles" (which includes flex fuel, hybrids and diesel) making up 49 percent of new vehicle sales by 2035. In 2008, this category only made up 13 percent. Why should we expect the increase? Higher CAFE standards and climbing fuel prices will force the issue.

The breakdown of this "alternative vehicles" category is interesting, too. In 2008, flex fuel vehicles made up around 80 percent of the total, with hybrid electrics making up most of the rest. By the time we get to 2035, the EIA says flex fuel vehicles will make up less than half of the category, with hybrids and diesels all growing to fill the gap. Plug-ins? Well, the EIA thinks they'll reach around five percent of the total market in 25 years. Thanks to Roy B. for the tip!

[Source: U.S. Energy Information Administration]