In the 1967 film classic The Graduate, an older friend gives then-young Dustin Hoffman one word of career advice: "plastics." Today, make that two words: "pond scum."

The dramatic drop in the price of oil - regular gasoline can now be had for $1.77 per gallon in Concord (maybe less by the time you read this) - may slow the switch to renewable fuels, but it won't prevent an eventual conversion to greener forms of energy. Virtually no one expects oil prices to remain low once the global economy rebounds. Nor can humans, if much of the planet is to remain habitable, afford to continue pumping climate-warming carbon dioxide into the atmosphere.

On Monday, Monitor reporters Amy Augustine and Karen Langley described two green fuel companies that hope to profit by selling locally made biodiesel. In Pittsfield, former Franklin mayor Tony Giunta and Sarandis Karathanasis, a co-owner of The Red Blazer in Concord, are turning used cooking oil from restaurants into home heating oil that sells for less than fuel oil. Their company, Amenico, was confident enough about the market for their product to buy the former Pittsfield tannery, and they expect eventually to employ 25 people.

Since the nation produces an estimated 10 billion gallons of waste vegetable oil every year, there's plenty of raw material available. It does, however, make us wonder whether whole neighborhoods will soon smell like chicken, french fries and doughnuts.

Though the official opening won't occur until Dec. 5, the state's first biodiesel gas station and convenience store is up and running in Dover. Simply Green, which also sells regular gasoline, gets 75 percent of its wares from within 100 miles of Dover. The lower the cost to transport a product, the lower its carbon footprint. And when customers buy locally produced goods, the money stays in the local economy.

Eventually, the station hopes to produce its own fuel locally as well, using what could prove to be the next major energy source: pond scum. Some algae are roughly 50 percent fat that can be converted to fuel in a process that, unlike most ethanol production, does not drive up food prices. Algae, since it's hyper-efficient, is also capable of producing anywhere from 30 to 100 times more fuel per acre than standard food crops.

Researchers are experimenting with lots of ways to produce algae efficiently and economically, ranging from simple outdoor ponds to elaborate arrays of tanks and tubes. In perhaps the most visionary operation to open so far, Arizona Public Service Company has teamed up with Greenfuel Technologies to build a bioreactor that uses the carbon dioxide emissions from one of the plant's smokestacks. The algae consume the C02, and the algae is then broken down, its fats into biodiesel, starches into ethanol, and protein into livestock feed. Algae can also be fed with agricultural runoff, farm manure or human waste, which reduces another problem.

Algae's potential is enormous. In 2006, UNH physics professor Michael Briggs estimated that the equivalent in biodiesel of all the transportation fuel used in the United States annually could be produced with 9.5 million acres of algal ponds. The nation, by comparison, has 450 million acres in crop lands.

The drop in crude oil prices is a godsend given the frightening economy. It's temporarily making alternative fuels less competitive. But it's also buying savvy pioneers like the investors in Amenico and Simply Green the time they need to perfect the energy sources of the future.