Petroleum is among the most common and best known fossil fuel sources. As easily extracted reserves are increasingly depleted, the era of cheap and plentiful oil is receding.
Petroleum is used in many industrial and chemical processes as well as for a fuel source. As many of the materials made from petroleum products cannot be manufactured otherwise nor replaced easily, conservation efforts must focus on ending use of petroleum in applications where it is easily replaceable.
The first step is to stop using petroleum as a fuel for vehicles. Brazil has pioneered use of ethanol as a major fuel component (over 90% of vehicles in Brazil use over 10% ethanol fuel blends). Electric vehicles and increased public transit are also solutions.
Another way to reduce global use of petroleum is for national policies to emphasize energy independence based on sustainable/renewable sources (rather than opening up wilderness to more risky and difficult drilling ion order to obtain a few weeks worth of oil).
Carbon trading strategies may also reduce reliance on all fossil fuels.