Clean machines.

Brazil's state-owned oil giant Petrobras and Rio de Janeiro's mass-transit company association, the Sindicato de Companhias, recently introduced a natural-gas project for the city's bus system. Ildo Sauer, Petrobras' gas and energy director, says the goal of the project is to prove the benefits of natural gas vehicles in urban transportation. Natural gas, which produces less pollution, is also cheaper than regular gasoline, so bus fares could be reduced as well. German auto giant Mercedes-Benz in Brazil made the first natural-gas bus for Rio, which is air conditioned and carries 40 seated passengers. The transit company Rubanil will operate the first bus. Although still in a testing stage, the project is expected to extend to 50,000 buses in metropolitan Rio.